Add bilingual day-label headers with Latin weekday/season/ordinal vocabulary

Builds every day label as a {en, la} pair (weekdays, ranks, season/ordinal
phrasing authored in Latin; proper names without an authored Latin form
fall back to their English string) and merges the date+day-label into one
header in the day-nav bar.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

TODO.md

@@ -27,6 +27,11 @@ across every hour and content type in this app.
 2. **Minimal-proof-done, bulk content pending** — mechanism is built and trusted (a proof
    date/entry already resolves correctly end-to-end); what's left is authoring/importing more
    content in that same shape across the rest of the calendar:
+   - Latin saint/octave/named-feast names for the bilingual date/day-label header (see
+     "Bilingual, merged date/day-label header" below) — the `{en, la}` mechanism is built and
+     every proper name falls back to English gracefully, but zero saints, octaves, or named
+     temporal feasts have an authored Latin name anywhere in `src/data/**`. Weekday names,
+     month names, rank labels, and season/ordinal phrasing already have real Latin.
    - Matins: bible-plan TSV bulk conversion is done (see "Bible-plan TSV — bulk conversion
      done" below) — not yet added to a test table, though (unlike sanctoral/temporal content)
      there's no reference breviary to spot-check this plan against by design. Still open:
@@ -2156,6 +2161,37 @@ Trinity" for their own last Sunday, where before the fix they'd shown four diffe
 Tests in `tests/calendar/day-label.test.ts` updated accordingly. `npm test` (365 tests) and
 `tsc --noEmit` both pass.
 
+### Bilingual, merged date/day-label header — done (2026-08-18)
+
+The civil date/weekday (`day-nav`'s date span) and the "day being celebrated" text
+(`getDayLabel`, previously repeated inside every hour's own view) are now merged into one
+header block in `day-nav.ts`, and both are bilingual. `getDayLabel()` returns
+`Partial<Record<string,string>>` (`{en, la}`) instead of a plain English string, matching
+`hours/types.ts`'s existing bilingual convention; `formatDateLong()` (`src/ui/format.ts`) is
+bilingual too, since `Intl` has no Latin locale data (`MONTH_LABELS_LA` authored directly).
+Latin weekday names are spelled out per direct instruction — "Feria Tertia", not "Feria III"
+— `Dominica`/`Feria Secunda`...`Sexta`/`Sabbato`. Advent and Lent specifically drop the
+redundant leading weekday word from `temporalLabel()` now that the header always shows the
+weekday on its own ("Tuesday in the 2nd week of Advent" → "In the 2nd week of Advent") — every
+other season (Epiphanytide, Eastertide, Trinitytide, the plain fallback) keeps its weekday
+prefix, a deliberate narrower-scope decision, not an oversight.
+
+**Real content gap, left open on purpose**: no Latin form exists anywhere for saint names
+(`SanctoralIdentity.name`), octave names, or named-temporal-feast names — only rank labels,
+weekday names, month names, and season/ordinal phrasing have authored Latin. Every saint/
+octave/feast name currently falls back to its English string as its own `la` value too (same
+"surface real text over missing" convention used elsewhere), so Latin mode never shows a blank
+where a proper name belongs — but it also means Latin mode still reads mostly-English for any
+day with a real winner. Authoring actual Latin names per saint/octave/feast is separate future
+content work (hundreds of records), not started here.
+
+`tests/calendar/day-label.test.ts` rewritten for the `{en, la}` shape (all `.en` values
+unchanged except the Advent/Lent weekday-drop cases), plus new representative `.la`
+assertions (weekday, rank, season-ordinal genitive construction, English-fallback-for-a-
+saint-name). `tests/hours/compline.test.ts` and `tests/ui/shell.test.ts` updated too. `npm
+test` (383 tests) and `tsc --noEmit` both pass; manually verified in the browser (English,
+Latin, and both-language modes) against an Advent date with an active octave.
+
 ## Known, deliberate simplifications (not bugs — working as designed)
 
 - `getDayCollects`: each collect in a multi-collect day renders as its own

src/calendar/day-label.ts

@@ -9,7 +9,16 @@
 // become a configurable choice later (the same day->id indirection
 // philosophy already used for the sanctoral calendar), not hardcoded here
 // forever — just not built yet.
-import type { FeastClass, LiturgicalDay, TemporalCategory } from './types';
+//
+// Bilingual: every label is built as a `Bi` (`{en, la}`) pair throughout.
+// Proper names (a saint's name, an octave's name, a named temporal feast's
+// name) have no authored Latin form anywhere in `data/` today — those use
+// the English string as their own `la` value too (same "surface real text
+// rather than block on missing" convention used elsewhere in this app),
+// rather than leaving Latin mode showing blanks. Only the closed,
+// mechanism-level vocabulary here (weekdays, ranks, season/ordinal
+// phrasing) has real Latin authored.
+import type { FeastClass, LiturgicalDay, TemporalCategory, Weekday } from './types';
 import { easterSunday } from './easter';
 import { adventStart, firstSundayStrictlyAfter, sundayOnOrBefore } from './temporal';
 import { addDays, daysBetween, toIsoDate } from './date-math';
@@ -17,6 +26,26 @@ import { getTemporalFeastRecord } from './temporal-feasts';
 import { activeOctavesFor, octaveGoverningPrivilegedDay, resolveActiveOctave, type ActiveOctave } from './octaves';
 import { resolveTemporalId } from './temporal-id';
 
+interface Bi {
+  en: string;
+  la: string;
+  [lang: string]: string;
+}
+
+function bi(en: string, la: string): Bi {
+  return { en, la };
+}
+
+/** A proper name with no authored Latin form yet — the English string
+ * stands in for `la` too. See file-header note. */
+function biFallback(name: string): Bi {
+  return { en: name, la: name };
+}
+
+function joinBi(items: Bi[], sep = ' — '): Bi {
+  return { en: items.map((i) => i.en).join(sep), la: items.map((i) => i.la).join(sep) };
+}
+
 function capitalize(text: string): string {
   return text.charAt(0).toUpperCase() + text.slice(1);
 }
@@ -38,6 +67,56 @@ function ordinal(n: number): string {
   }
 }
 
+// Feminine Latin ordinal adjectives (agreeing with "Dominica"/"Hebdomada"/
+// "die", all feminine) — covers 1st through 24th, the full range this app
+// ever counts to (Trinitytide's fixed last week is the 23rd). Not a general
+// Latin-numerals utility, just this app's own closed display vocabulary.
+const ORDINAL_LA = [
+  '',
+  'prima',
+  'secunda',
+  'tertia',
+  'quarta',
+  'quinta',
+  'sexta',
+  'septima',
+  'octava',
+  'nona',
+  'decima',
+  'undecima',
+  'duodecima',
+  'decima tertia',
+  'decima quarta',
+  'decima quinta',
+  'decima sexta',
+  'decima septima',
+  'decima octava',
+  'decima nona',
+  'vicesima',
+  'vicesima prima',
+  'vicesima secunda',
+  'vicesima tertia',
+  'vicesima quarta',
+];
+
+function ordinalLa(n: number): string {
+  return ORDINAL_LA[n] ?? `${n}a`;
+}
+
+const WEEKDAY_LABELS: Record<Weekday, Bi> = {
+  sunday: bi('Sunday', 'Dominica'),
+  monday: bi('Monday', 'Feria Secunda'),
+  tuesday: bi('Tuesday', 'Feria Tertia'),
+  wednesday: bi('Wednesday', 'Feria Quarta'),
+  thursday: bi('Thursday', 'Feria Quinta'),
+  friday: bi('Friday', 'Feria Sexta'),
+  saturday: bi('Saturday', 'Sabbato'),
+};
+
+function weekdayLabel(day: LiturgicalDay): Bi {
+  return WEEKDAY_LABELS[day.weekday];
+}
+
 interface OrdinalSeason {
   /** ISO date of the season's own anchor day, for a given calendar year. */
   anchorDate(year: number): string;
@@ -45,10 +124,16 @@ interface OrdinalSeason {
    * Lent: the anchor is its own named day, excluded from the count — the
    * numbered weeks start the following Sunday. */
   includeAnchorWeek: boolean;
-  /** Used in "Weekday after {anchorName}" for the anchor's own partial week. */
-  anchorName: string;
-  /** Used in "the Nth Sunday/week {preposition} {ordinalName}". */
-  ordinalName: string;
+  /** Used in "Weekday after {anchorName}" for the anchor's own partial week,
+   * and as the anchor day's own standalone name. */
+  anchorName: Bi;
+  /** Used in "the Nth Sunday/week {preposition} {ordinalName}". For
+   * `preposition: 'of'`, `ordinalName.la` is already the correct genitive
+   * form (glued directly after the ordinal, no linking word — Latin
+   * idiom). For `preposition: 'after'`, `ordinalName.la` is the form used
+   * after "post" (traditionally accusative, or an idiomatic fixed phrase
+   * like "post Cineres"). */
+  ordinalName: Bi;
   preposition: 'after' | 'of';
   /** The season's own anchor day's rank, if it sits on the closed
    * pre-1955 duplex scale at all — Ash Wednesday (Lent's anchor) doesn't;
@@ -56,44 +141,61 @@ interface OrdinalSeason {
    * and shows no parenthetical, same "omit rather than guess" convention
    * `formatRank`/`status` fields use elsewhere. */
   anchorRank?: FeastClass;
+  /** Advent and Lent only: once the header always shows the day's weekday
+   * on its own, repeating it at the front of this label is redundant — so
+   * those two seasons drop it here, in both languages. Every other season
+   * keeps the weekday prefix (explicit, narrower scope decision). */
+  dropWeekdayPrefix?: boolean;
 }
 
 const ORDINAL_SEASONS: Partial<Record<string, OrdinalSeason>> = {
   advent: {
     anchorDate: adventStart,
     includeAnchorWeek: true,
-    anchorName: 'Advent',
-    ordinalName: 'Advent',
+    anchorName: bi('Advent', 'Adventus'),
+    // Genitive of 4th-declension "adventus" is also "Adventus" — no
+    // linking word needed: "Hebdomada II Adventus".
+    ordinalName: bi('Advent', 'Adventus'),
     preposition: 'of',
+    dropWeekdayPrefix: true,
   },
   epiphanytide: {
     anchorDate: (year) => `${year}-01-06`,
     includeAnchorWeek: false,
-    anchorName: 'Epiphany',
-    ordinalName: 'Epiphany',
+    anchorName: bi('Epiphany', 'Epiphania'),
+    // Accusative, for "post Epiphaniam".
+    ordinalName: bi('Epiphany', 'Epiphaniam'),
     preposition: 'after',
     anchorRank: 'duplex-1-classis',
   },
   lent: {
     anchorDate: (year) => addDays(toIsoDate(easterSunday(year)), -46),
     includeAnchorWeek: false,
-    anchorName: 'Ash Wednesday',
-    ordinalName: 'Lent',
+    anchorName: bi('Ash Wednesday', 'Feria Quarta Cinerum'),
+    // Genitive of 1st-declension "Quadragesima": "Hebdomada II
+    // Quadragesimae". The pre-Lent-I days use the real traditional idiom
+    // "post Cineres" instead (see temporalLabel below), not this field.
+    ordinalName: bi('Lent', 'Quadragesimae'),
     preposition: 'of',
+    dropWeekdayPrefix: true,
   },
   eastertide: {
     anchorDate: (year) => toIsoDate(easterSunday(year)),
     includeAnchorWeek: false,
-    anchorName: 'Easter',
-    ordinalName: 'Easter',
+    anchorName: bi('Easter', 'Pascha'),
+    // "Pascha" is indeclinable — same form after "post".
+    ordinalName: bi('Easter', 'Pascha'),
     preposition: 'after',
     anchorRank: 'duplex-1-classis',
   },
   trinitytide: {
     anchorDate: (year) => addDays(toIsoDate(easterSunday(year)), 56),
     includeAnchorWeek: false,
-    anchorName: 'Trinity Sunday',
-    ordinalName: 'Trinity',
+    anchorName: bi('Trinity Sunday', 'Dominica Sanctissimae Trinitatis'),
+    // Accusative, for "post Sanctissimam Trinitatem" — this app's own
+    // Trinity-counted convention (see file header), not the historical
+    // Pentecost-counted "post Pentecosten".
+    ordinalName: bi('Trinity', 'Sanctissimam Trinitatem'),
     preposition: 'after',
     anchorRank: 'duplex-1-classis',
   },
@@ -107,14 +209,16 @@ const ORDINAL_SEASONS: Partial<Record<string, OrdinalSeason>> = {
  * octave, but nobody calls it that). Advent's own anchor (Advent I Sunday)
  * doesn't take this branch — it's already "the 1st Sunday of Advent" via
  * the ordinal path below. */
-function anchorDayName(day: LiturgicalDay, withRank = true): string | undefined {
+function anchorDayName(day: LiturgicalDay, withRank = true): Bi | undefined {
   const config = ORDINAL_SEASONS[day.season];
   if (!config || config.includeAnchorWeek) {
     return undefined;
   }
   const year = Number(day.date.slice(0, 4));
   if (day.date === config.anchorDate(year)) {
-    return withRank && config.anchorRank ? `${config.anchorName} (${formatRank(config.anchorRank)})` : config.anchorName;
+    return withRank && config.anchorRank
+      ? bi(`${config.anchorName.en} (${formatRank(config.anchorRank).en})`, `${config.anchorName.la} (${formatRank(config.anchorRank).la})`)
+      : config.anchorName;
   }
   return undefined;
 }
@@ -147,47 +251,57 @@ const FIXED_LAST_SUNDAY_ORDINAL = 23;
  *     every year, not just overflow ones.
  * Only ever fires within trinitytide, since that's the only season
  * resolveTemporalId can return either of these ids for a date outside
- * their own native season.
+ * their own native season. Trinitytide isn't in the weekday-drop set, so
+ * both languages keep their weekday prefix here.
  */
-function trinitytideOverrideLabel(day: LiturgicalDay): string | undefined {
+function trinitytideOverrideLabel(day: LiturgicalDay): Bi | undefined {
   if (day.season !== 'trinitytide') {
     return undefined;
   }
   const id = resolveTemporalId(day.date);
-  const weekdayName = capitalize(day.weekday);
+  const weekdayName = weekdayLabel(day);
 
   const epiphanyMatch = id.match(/^post-epiphany-(\d)$/);
   if (epiphanyMatch) {
     const n = Number(epiphanyMatch[1]);
     return day.weekday === 'sunday'
-      ? `The ${ordinal(n)} Sunday after Epiphany`
-      : `${weekdayName} in the ${ordinal(n)} week after Epiphany`;
+      ? bi(`The ${ordinal(n)} Sunday after Epiphany`, `Dominica ${ordinalLa(n)} post Epiphaniam`)
+      : bi(`${weekdayName.en} in the ${ordinal(n)} week after Epiphany`, `${weekdayName.la} in hebdomada ${ordinalLa(n)} post Epiphaniam`);
   }
 
   if (id === 'post-pentecost-24') {
     return day.weekday === 'sunday'
-      ? `The ${ordinal(FIXED_LAST_SUNDAY_ORDINAL)} Sunday after Trinity`
-      : `${weekdayName} in the ${ordinal(FIXED_LAST_SUNDAY_ORDINAL)} week after Trinity`;
+      ? bi(
+          `The ${ordinal(FIXED_LAST_SUNDAY_ORDINAL)} Sunday after Trinity`,
+          `Dominica ${ordinalLa(FIXED_LAST_SUNDAY_ORDINAL)} post Sanctissimam Trinitatem`,
+        )
+      : bi(
+          `${weekdayName.en} in the ${ordinal(FIXED_LAST_SUNDAY_ORDINAL)} week after Trinity`,
+          `${weekdayName.la} in hebdomada ${ordinalLa(FIXED_LAST_SUNDAY_ORDINAL)} post Sanctissimam Trinitatem`,
+        );
   }
 
   return undefined;
 }
 
-function temporalLabel(day: LiturgicalDay): string {
+function temporalLabel(day: LiturgicalDay): Bi {
   const trinitytideOverride = trinitytideOverrideLabel(day);
   if (trinitytideOverride) {
     return trinitytideOverride;
   }
 
-  const weekdayName = capitalize(day.weekday);
+  const weekdayName = weekdayLabel(day);
   const config = ORDINAL_SEASONS[day.season];
   if (!config) {
     // No ordinal convention modeled for this season (Septuagesima-tide,
     // Passiontide, Ascensiontide, Pentecost, Christmastide, the
     // Corpus-Christi/Sacred-Heart single-day seasons) — their few days
     // mostly have their own proper names rather than ordinal counting, so
-    // this fallback is expected to be seen, not a gap to fill later.
-    return `${weekdayName} in ${capitalize(day.season.replace(/-/g, ' '))}`;
+    // this fallback is expected to be seen, not a gap to fill later. No
+    // authored Latin season name exists for these yet, so `la` falls back
+    // to the same English season word.
+    const seasonName = capitalize(day.season.replace(/-/g, ' '));
+    return bi(`${weekdayName.en} in ${seasonName}`, `${weekdayName.la} in ${seasonName}`);
   }
 
   const year = Number(day.date.slice(0, 4));
@@ -199,34 +313,54 @@ function temporalLabel(day: LiturgicalDay): string {
 
   const firstNumberedSunday = config.includeAnchorWeek ? anchor : firstSundayStrictlyAfter(anchor);
   if (day.date < firstNumberedSunday) {
-    return `${weekdayName} after ${config.anchorName}`;
+    // Lent's own pre-Lent-I days use the real traditional idiom "post
+    // Cineres" rather than the season's genitive `ordinalName` (which is
+    // built for the "of Lent" construction, not "after Ash Wednesday").
+    const afterAnchorLa = day.season === 'lent' ? 'Cineres' : config.anchorName.la;
+    return config.dropWeekdayPrefix
+      ? bi(`After ${config.anchorName.en}`, `Post ${afterAnchorLa}`)
+      : bi(`${weekdayName.en} after ${config.anchorName.en}`, `${weekdayName.la} post ${afterAnchorLa}`);
   }
 
   const weeksSince = daysBetween(firstNumberedSunday, sundayOnOrBefore(day.date)) / 7;
   const ordinalStr = ordinal(weeksSince + 1);
+  const ordinalStrLa = ordinalLa(weeksSince + 1);
   if (day.weekday === 'sunday') {
-    return `The ${ordinalStr} Sunday ${config.preposition} ${config.ordinalName}`;
+    return config.preposition === 'of'
+      ? bi(`The ${ordinalStr} Sunday of ${config.ordinalName.en}`, `Dominica ${ordinalStrLa} ${config.ordinalName.la}`)
+      : bi(`The ${ordinalStr} Sunday after ${config.ordinalName.en}`, `Dominica ${ordinalStrLa} post ${config.ordinalName.la}`);
   }
-  return `${weekdayName} in the ${ordinalStr} week ${config.preposition} ${config.ordinalName}`;
+  const weekPhraseLa =
+    config.preposition === 'of' ? `hebdomada ${ordinalStrLa} ${config.ordinalName.la}` : `hebdomada ${ordinalStrLa} post ${config.ordinalName.la}`;
+  return config.dropWeekdayPrefix
+    ? bi(`In the ${ordinalStr} week ${config.preposition} ${config.ordinalName.en}`, `In ${weekPhraseLa}`)
+    : bi(`${weekdayName.en} in the ${ordinalStr} week ${config.preposition} ${config.ordinalName.en}`, `${weekdayName.la} in ${weekPhraseLa}`);
 }
 
 /** "Third Day within the Octave of St. Lawrence" for an ordinary mid-octave
- * day (e.g. "Tertia die infra Octavam S. Laurentii Martyris"), or plain
- * "Octave of St. Lawrence" for the octave's own closing day — real DO
- * Latin distinguishes "infra octavam" (within the octave, days 2-7) from
- * "in octava" (on the octave day itself, day 8), live-verified: Aug 17
- * (St. Lawrence's closing day) titles itself "In Octava S. Laurentii
- * Martyris", not "Octava die infra Octavam...". Day 1 shouldn't normally
- * reach either branch (that day's own winner is the feast itself, handled
- * above before this is ever called) — kept simple rather than
- * special-cased for that rare edge case (see applyOctaves's own
- * `isOwnStartDay` comment in calendar/index.ts for when it can happen). */
-function octaveCoreName(octave: ActiveOctave): string {
-  return octave.isClosingDay ? `Octave of ${octave.name}` : `${ordinal(octave.dayNumber)} Day within the Octave of ${octave.name}`;
+ * day ("Tertia die infra Octavam S. Laurentii Martyris"), or plain "Octave
+ * of St. Lawrence" for the octave's own closing day ("In Octava S.
+ * Laurentii Martyris") — real DO Latin distinguishes "infra octavam"
+ * (within the octave, days 2-7) from "in octava" (on the octave day
+ * itself, day 8), live-verified: Aug 17 (St. Lawrence's closing day)
+ * titles itself "In Octava S. Laurentii Martyris", not "Octava die infra
+ * Octavam...". Day 1 shouldn't normally reach either branch (that day's
+ * own winner is the feast itself, handled above before this is ever
+ * called) — kept simple rather than special-cased for that rare edge case
+ * (see applyOctaves's own `isOwnStartDay` comment in calendar/index.ts for
+ * when it can happen). The octave's own `name` has no authored Latin form
+ * (see file header), so both languages currently show the same name text
+ * — only the surrounding phrasing differs. */
+function octaveCoreName(octave: ActiveOctave): Bi {
+  return octave.isClosingDay
+    ? bi(`Octave of ${octave.name}`, `In Octava ${octave.name}`)
+    : bi(`${ordinal(octave.dayNumber)} Day within the Octave of ${octave.name}`, `${ordinalLa(octave.dayNumber)} die infra Octavam ${octave.name}`);
 }
 
-function octaveLabel(octave: ActiveOctave): string {
-  return `${octaveCoreName(octave)} (${formatRank(octave.wins)})`;
+function octaveLabel(octave: ActiveOctave): Bi {
+  const core = octaveCoreName(octave);
+  const rank = formatRank(octave.wins);
+  return bi(`${core.en} (${rank.en})`, `${core.la} (${rank.la})`);
 }
 
 /** Same phrasing as `octaveLabel`, but without the parenthesized rank —
@@ -238,7 +372,7 @@ function octaveLabel(octave: ActiveOctave): string {
  * it *won as*, not a fact worth restating once a duplex-or-higher saint
  * has displaced it and it's just riding along as a commemoration
  * instead). */
-function octaveCommemorationLabel(octave: ActiveOctave): string {
+function octaveCommemorationLabel(octave: ActiveOctave): Bi {
   return octaveCoreName(octave);
 }
 
@@ -258,7 +392,8 @@ function octaveCommemorationLabel(octave: ActiveOctave): string {
  * - `sanctoral`: every commemorated saint, plain name, no rank (multiple
  *   real ones can coexist — e.g. two colliding saints on the same date —
  *   this app's own "generous commemorations" design keeps every one of
- *   them, not just the first).
+ *   them, not just the first). No authored Latin saint names exist yet
+ *   (see file header), so `la` falls back to the same English name.
  * - `temporal`: the day's own real Sunday/feria identity, if
  *   `decideOccurrence` demoted it to a commemoration (`ordinary-sunday`/
  *   `privileged-feria`/`privileged-feria-minor`) — matched by id against
@@ -282,35 +417,35 @@ function octaveCommemorationLabel(octave: ActiveOctave): string {
 function collectCommemorations(
   day: LiturgicalDay,
   opts: { showOctaves: boolean; excludeOctaveId?: string },
-): { sanctoral: string[]; temporal: string[]; octaves: string[] } {
+): { sanctoral: Bi[]; temporal: Bi[]; octaves: Bi[] } {
   const temporalId = resolveTemporalId(day.date);
   const activeOctaves = opts.showOctaves ? activeOctavesFor(day.date) : [];
-  const sanctoral: string[] = [];
-  const temporal: string[] = [];
-  const octaves: string[] = [];
+  const sanctoral: Bi[] = [];
+  const temporal: Bi[] = [];
+  const octaves: Bi[] = [];
   for (const c of day.commemorations) {
     if (c.kind === 'sanctoral') {
-      sanctoral.push(c.name);
+      sanctoral.push(biFallback(c.name));
     } else if (c.kind === 'temporal') {
       if (c.id === temporalId) {
         temporal.push(anchorDayName(day, false) ?? temporalLabel(day));
       }
     } else if (opts.showOctaves && c.id !== opts.excludeOctaveId) {
       const octave = activeOctaves.find((a) => a.id === c.id);
-      octaves.push(octave ? octaveCommemorationLabel(octave) : c.name);
+      octaves.push(octave ? octaveCommemorationLabel(octave) : biFallback(c.name));
     }
   }
   return { sanctoral, temporal, octaves };
 }
 
-const RANK_LABELS: Record<FeastClass, string> = {
-  simplex: 'Simplex',
-  vigil: 'Vigil',
-  semiduplex: 'Semiduplex',
-  duplex: 'Duplex',
-  'duplex-majus': 'Duplex Majus',
-  'duplex-2-classis': 'Duplex II Class',
-  'duplex-1-classis': 'Duplex I Class',
+const RANK_LABELS: Record<FeastClass, Bi> = {
+  simplex: bi('Simplex', 'Simplex'),
+  vigil: bi('Vigil', 'Vigilia'),
+  semiduplex: bi('Semiduplex', 'Semiduplex'),
+  duplex: bi('Duplex', 'Duplex'),
+  'duplex-majus': bi('Duplex Majus', 'Duplex Majus'),
+  'duplex-2-classis': bi('Duplex II Class', 'Duplex II. Classis'),
+  'duplex-1-classis': bi('Duplex I Class', 'Duplex I. Classis'),
 };
 
 /** The day's own winning saint's rank, parenthesized after their name —
@@ -318,7 +453,7 @@ const RANK_LABELS: Record<FeastClass, string> = {
  * saint. Only the day's own *winner* gets this treatment, not every
  * commemoration, matching the "winner is primary, commemorations are
  * secondary" distinction this file already draws throughout. */
-function formatRank(rank: FeastClass): string {
+function formatRank(rank: FeastClass): Bi {
   return RANK_LABELS[rank];
 }
 
@@ -330,14 +465,15 @@ function formatRank(rank: FeastClass): string {
  * Semiduplex regardless of whether it's additionally "privileged"
  * (privilege is about resisting supersession, a property of
  * `temporalCategory`, not a higher spot on the duplex scale) — so both
- * Sunday categories share one label here. */
-const TEMPORAL_CATEGORY_RANK_LABELS: Record<TemporalCategory, string> = {
-  'ordinary-sunday': 'Semiduplex',
-  'privileged-sunday': 'Semiduplex',
-  'ordinary-feria': 'Feria',
-  'privileged-feria-minor': 'Feria',
-  'privileged-feria': 'Feria',
-  'privileged-feria-major': 'Feria',
+ * Sunday categories share one label here. Both "Semiduplex" and "Feria"
+ * are already the real Latin words, so `en`/`la` coincide here too. */
+const TEMPORAL_CATEGORY_RANK_LABELS: Record<TemporalCategory, Bi> = {
+  'ordinary-sunday': bi('Semiduplex', 'Semiduplex'),
+  'privileged-sunday': bi('Semiduplex', 'Semiduplex'),
+  'ordinary-feria': bi('Feria', 'Feria'),
+  'privileged-feria-minor': bi('Feria', 'Feria'),
+  'privileged-feria': bi('Feria', 'Feria'),
+  'privileged-feria-major': bi('Feria', 'Feria'),
 };
 
 /**
@@ -348,9 +484,12 @@ const TEMPORAL_CATEGORY_RANK_LABELS: Record<TemporalCategory, string> = {
  * eligible to ride along with it. Each branch below only decides two
  * things: what the primary label is, and what commemoration *groups* are
  * eligible here and in what order — the actual filtering/formatting work
- * is `collectCommemorations`'s alone, shared by every branch.
+ * is `collectCommemorations`'s alone, shared by every branch. Returns a
+ * `Partial<Record<string, string>>` keyed by language code (`en`/`la`),
+ * the same convention `hours/types.ts`'s `ResolvedText`/`ResolvedVerse`
+ * already use.
  */
-export function getDayLabel(day: LiturgicalDay): string {
+export function getDayLabel(day: LiturgicalDay): Partial<Record<string, string>> {
   if (day.winner.kind === 'sanctoral') {
     // Octaves only ride along here on `ordinary-feria` — a day with real
     // standing of its own (a Sunday, a privileged feria) doesn't mention
@@ -362,8 +501,10 @@ export function getDayLabel(day: LiturgicalDay): string {
     const { sanctoral, temporal, octaves } = collectCommemorations(day, {
       showOctaves: day.temporalCategory === 'ordinary-feria',
     });
-    const winnerName = `${day.winner.name} (${formatRank(day.winner.rank)})`;
-    return [winnerName, ...temporal, ...sanctoral, ...octaves].join(' — ');
+    const rank = formatRank(day.winner.rank);
+    const winnerName = biFallback(day.winner.name);
+    const winner = bi(`${winnerName.en} (${rank.en})`, `${winnerName.la} (${rank.la})`);
+    return joinBi([winner, ...temporal, ...sanctoral, ...octaves]);
   }
 
   // A named temporal feast (Christmas, Pentecost, Marian Saturday, ...)
@@ -373,9 +514,12 @@ export function getDayLabel(day: LiturgicalDay): string {
   // temporal-feasts.ts) and fall through further down.
   const namedFeast = getTemporalFeastRecord(day.winner.id);
   if (namedFeast) {
-    const primary = namedFeast.rank ? `${namedFeast.name} (${formatRank(namedFeast.rank)})` : namedFeast.name;
+    const name = biFallback(namedFeast.name);
+    const primary = namedFeast.rank
+      ? bi(`${name.en} (${formatRank(namedFeast.rank).en})`, `${name.la} (${formatRank(namedFeast.rank).la})`)
+      : name;
     const { sanctoral } = collectCommemorations(day, { showOctaves: false });
-    return [primary, ...sanctoral].join(' — ');
+    return joinBi([primary, ...sanctoral]);
   }
 
   // A season's own named anchor day (Trinity Sunday, Easter, Ash
@@ -388,7 +532,7 @@ export function getDayLabel(day: LiturgicalDay): string {
   const anchorName = anchorDayName(day);
   if (anchorName) {
     const { sanctoral } = collectCommemorations(day, { showOctaves: false });
-    return [...sanctoral, anchorName].join(' — ');
+    return joinBi([...sanctoral, anchorName]);
   }
 
   // An active octave (St. Lawrence's, ...) is this day's real primary
@@ -424,10 +568,12 @@ export function getDayLabel(day: LiturgicalDay): string {
   if (activeOctave) {
     const { sanctoral, octaves } = collectCommemorations(day, { showOctaves: true, excludeOctaveId: activeOctave.id });
     const primary = octaveLabel(activeOctave);
-    return [primary, ...octaves, ...sanctoral].join(' — ');
+    return joinBi([primary, ...octaves, ...sanctoral]);
   }
 
-  const temporal = `${temporalLabel(day)} (${TEMPORAL_CATEGORY_RANK_LABELS[day.temporalCategory]})`;
+  const temporalRank = TEMPORAL_CATEGORY_RANK_LABELS[day.temporalCategory];
+  const label = temporalLabel(day);
+  const temporal = bi(`${label.en} (${temporalRank.en})`, `${label.la} (${temporalRank.la})`);
   const { sanctoral } = collectCommemorations(day, { showOctaves: false });
-  return [...sanctoral, temporal].join(' — ');
+  return joinBi([...sanctoral, temporal]);
 }

src/hours/types.ts

@@ -269,11 +269,11 @@ export interface ResolvedOrdo {
   /** Set when this hour hasn't been built yet — UI shows "coming soon" instead of empty content. */
   notImplemented?: true;
   /**
-   * "Monday in the 10th week after Trinity", "St. Ereden — ...", etc. —
-   * see calendar/day-label.ts. Computed from whichever LiturgicalDay the
-   * hour actually resolved against, which can differ from `date` itself
-   * (Compline may anticipate tomorrow — see calendar/vespers.ts). Absent
-   * on not-yet-built hours.
+   * "Monday in the 10th week after Trinity", "St. Ereden — ...", etc.,
+   * keyed by language code (`en`/`la`) — see calendar/day-label.ts.
+   * Computed from whichever LiturgicalDay the hour actually resolved
+   * against, which can differ from `date` itself (Compline may anticipate
+   * tomorrow — see calendar/vespers.ts). Absent on not-yet-built hours.
    */
-  dayLabel?: string;
+  dayLabel?: Partial<Record<string, string>>;
 }

src/ui/day-nav.ts

@@ -1,13 +1,28 @@
 import { getState, shiftDate, goToToday } from '../app-state';
-import { formatDateLong } from './format';
+import { resolveDay } from '../calendar';
+import { getDayLabel } from '../calendar/day-label';
+import { formatDateLong, renderBilingual } from './format';
 
+/** Renders navigation plus the merged "when" header: the civil date/
+ * weekday and the liturgical day-being-celebrated, together in one place
+ * — previously the date lived here while the day-being-celebrated text
+ * was repeated separately inside every hour's own view. The day-being-
+ * celebrated text is hour-independent (the same LiturgicalDay for every
+ * hour on a given date), so it's resolved directly here via `resolveDay`
+ * rather than through any particular hour's `resolveOrdo`. */
 export function renderDayNav(container: HTMLElement): void {
-  const { date } = getState();
+  const { date, languages } = getState();
+  const day = resolveDay(date);
+  const dateLabel = formatDateLong(date);
+  const dayLabel = getDayLabel(day);
   container.innerHTML = `
     <nav class="day-nav" aria-label="Day navigation">
       <button type="button" class="day-nav-btn" data-action="prev" aria-label="Previous day">&larr;</button>
       <button type="button" class="day-nav-btn day-nav-today" data-action="today">Today</button>
-      <span class="day-nav-date">${formatDateLong(date)}</span>
+      <div class="day-nav-header">
+        ${renderBilingual(dateLabel, languages, 'day-nav-date')}
+        ${renderBilingual(dayLabel, languages, 'day-nav-label')}
+      </div>
       <button type="button" class="day-nav-btn" data-action="next" aria-label="Next day">&rarr;</button>
     </nav>
   `;

src/ui/format.ts

@@ -1,17 +1,62 @@
-/** Formats an ISO date as e.g. "Sunday, August 9, 2026" — always in UTC so
- * it matches calendar/weekday.ts's interpretation regardless of the
- * viewer's local timezone. */
-export function formatDateLong(isoDate: string): string {
+// Latin month names have no Intl locale data, so the genitive forms below
+// (used the same way English "of August" would be, e.g. "18 Augusti 2026")
+// are authored directly here.
+const MONTH_LABELS_LA = [
+  'Ianuarii',
+  'Februarii',
+  'Martii',
+  'Aprilis',
+  'Maii',
+  'Iunii',
+  'Iulii',
+  'Augusti',
+  'Septembris',
+  'Octobris',
+  'Novembris',
+  'Decembris',
+];
+
+const WEEKDAY_LABELS_LA = ['Dominica', 'Feria Secunda', 'Feria Tertia', 'Feria Quarta', 'Feria Quinta', 'Feria Sexta', 'Sabbato'];
+
+/** Formats an ISO date as e.g. "Sunday, August 9, 2026" (`en`) / "Dominica,
+ * die 9 Augusti 2026" (`la`) — always in UTC so it matches
+ * calendar/weekday.ts's interpretation regardless of the viewer's local
+ * timezone. Weekday naming mirrors calendar/day-label.ts's own
+ * `WEEKDAY_LABELS` (spelled-out Latin ferial names, not roman numerals). */
+export function formatDateLong(isoDate: string): Partial<Record<string, string>> {
   const date = new Date(`${isoDate}T00:00:00Z`);
-  return new Intl.DateTimeFormat('en-US', {
+  const en = new Intl.DateTimeFormat('en-US', {
     weekday: 'long',
     year: 'numeric',
     month: 'long',
     day: 'numeric',
     timeZone: 'UTC',
   }).format(date);
+
+  const day = date.getUTCDate();
+  const month = MONTH_LABELS_LA[date.getUTCMonth()];
+  const year = date.getUTCFullYear();
+  const weekday = WEEKDAY_LABELS_LA[date.getUTCDay()];
+  const la = `${weekday}, die ${day} ${month} ${year}`;
+
+  return { en, la };
 }
 
 export function hourLabel(hourId: string): string {
   return hourId.charAt(0).toUpperCase() + hourId.slice(1);
 }
+
+function escapeHtml(value: string): string {
+  return value.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;');
+}
+
+/** Renders one `<div class="lang-column">` per currently-active language
+ * for a bilingual text map — the same pattern hour-view.ts's own
+ * `renderColumns` uses for resolved liturgical text, shared here so
+ * day-nav.ts's header can reuse it instead of re-implementing it. */
+export function renderBilingual(text: Partial<Record<string, string>>, languages: readonly string[], className: string): string {
+  const cols = languages
+    .map((lang) => `<div class="lang-column" lang="${lang}">${escapeHtml(text[lang] ?? '')}</div>`)
+    .join('');
+  return `<div class="${className} lang-columns lang-columns-${languages.length}">${cols}</div>`;
+}

src/ui/hour-view.ts

@@ -149,7 +149,6 @@ export function renderHourView(container: HTMLElement): void {
   container.innerHTML = `
     <div class="hour-view">
       <h2>${hourLabel(selectedHour)}</h2>
-      ${ordo.dayLabel ? `<p class="day-label">${escapeHtml(ordo.dayLabel)}</p>` : ''}
       ${ordo.parts.map((part) => renderPart(part, languages)).join('')}
     </div>
   `;

src/ui/styles.css

@@ -165,12 +165,26 @@ button:focus-visible {
   cursor: pointer;
 }
 
-.day-nav-date {
-  font-weight: 600;
+.day-nav-header {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 0.15rem;
   min-width: 16rem;
   text-align: center;
 }
 
+.day-nav-date {
+  font-weight: 600;
+}
+
+.day-nav-label {
+  font-family: var(--font-ui);
+  font-size: 0.85rem;
+  font-style: italic;
+  color: var(--color-brass);
+}
+
 /* --------------------------------------------------------------------------
    Layout: hour list + hour view
    -------------------------------------------------------------------------- */
@@ -261,14 +275,6 @@ button:focus-visible {
   margin: 0 0 var(--space-1);
 }
 
-.day-label {
-  font-family: var(--font-ui);
-  font-size: 0.9em;
-  font-style: italic;
-  color: var(--color-brass);
-  margin: 0 0 var(--space-2);
-}
-
 .ordo-part-citation {
   font-family: var(--font-ui);
   font-size: 0.85em;

tests/calendar/christ-the-king.test.ts

@@ -16,7 +16,7 @@ describe('Christ the King (applyChristTheKing)', () => {
     // already carrying (Ss. Chrysanthus and Daria, Simplex, per the next
     // test below) -- this app's day label now surfaces every commemorated
     // saint, not just the Sunday itself.
-    expect(getDayLabel(day)).toBe('Christ the King (Duplex I Class) — Ss. Chrysanthus and Daria, Martyrs');
+    expect(getDayLabel(day).en).toBe('Christ the King (Duplex I Class) — Ss. Chrysanthus and Daria, Martyrs');
   });
 
   it('preserves a nested commemoration: a Simplex saint already commemorated under the ordinary Sunday stays commemorated', () => {

tests/calendar/day-label.test.ts

@@ -10,8 +10,11 @@ describe('getDayLabel — ordinal temporal label', () => {
     // the full-year sanctoral import), which would win outright and hide
     // this purely-temporal label case. 2027's Trinity Sunday is May 23,
     // so Trinity Monday is May 24 -- free of any sanctoral entry.
-    expect(getDayLabel(resolveDay('2027-05-24'))).toBe('Monday after Trinity Sunday (Feria)');
-    expect(getDayLabel(resolveDay('2026-01-07'))).toBe('Wednesday after Epiphany (Feria)'); // Epiphany 2026 is a Tuesday
+    expect(getDayLabel(resolveDay('2027-05-24')).en).toBe('Monday after Trinity Sunday (Feria)');
+    expect(getDayLabel(resolveDay('2026-01-07')).en).toBe('Wednesday after Epiphany (Feria)'); // Epiphany 2026 is a Tuesday
+    // Latin: spelled-out ferial weekday name (not roman numerals) and the
+    // "Feria" rank label, which is already the real Latin word.
+    expect(getDayLabel(resolveDay('2027-05-24')).la).toBe('Feria Secunda post Dominica Sanctissimae Trinitatis (Feria)');
   });
 
   it('names the anchor day itself, not "day after itself"', () => {
@@ -27,11 +30,20 @@ describe('getDayLabel — ordinal temporal label', () => {
     // commemorated in return (`decideOccurrence`'s own `ordinary-sunday`
     // branch), by bare name only — a commemoration never carries a rank
     // parenthetical, only the day's own winner does.
-    expect(getDayLabel(resolveDay('2026-05-31'))).toBe(
+    expect(getDayLabel(resolveDay('2026-05-31')).en).toBe(
       'The Queenship of the Blessed Virgin Mary (Duplex II Class) — Trinity Sunday',
     );
-    expect(getDayLabel(resolveDay('2026-04-05'))).toBe('Easter (Duplex I Class)');
-    expect(getDayLabel(resolveDay('2026-02-18'))).toBe('Ash Wednesday');
+    expect(getDayLabel(resolveDay('2026-04-05')).en).toBe('Easter (Duplex I Class)');
+    expect(getDayLabel(resolveDay('2026-02-18')).en).toBe('Ash Wednesday');
+    // Latin: no authored Latin saint name exists yet, so the winner's name
+    // falls back to the same English string (see file header) — only the
+    // rank label ("Duplex II. Classis") and the commemorated Sunday's own
+    // name ("Dominica Sanctissimae Trinitatis") are real Latin.
+    expect(getDayLabel(resolveDay('2026-05-31')).la).toBe(
+      'The Queenship of the Blessed Virgin Mary (Duplex II. Classis) — Dominica Sanctissimae Trinitatis',
+    );
+    expect(getDayLabel(resolveDay('2026-04-05')).la).toBe('Pascha (Duplex I. Classis)');
+    expect(getDayLabel(resolveDay('2026-02-18')).la).toBe('Feria Quarta Cinerum');
   });
 
   it('gives the correct week-after-Trinity ordinal', () => {
@@ -40,7 +52,7 @@ describe('getDayLabel — ordinal temporal label', () => {
     // sanctoral import), which wins outright. 2027's Trinity Sunday is
     // May 23, so 5 full weeks after the first Sunday-after-Trinity
     // (May 30) is Jun 28 -- free of any sanctoral entry.
-    expect(getDayLabel(resolveDay('2027-06-28'))).toBe('Monday in the 5th week after Trinity (Feria)');
+    expect(getDayLabel(resolveDay('2027-06-28')).en).toBe('Monday in the 5th week after Trinity (Feria)');
   });
 
   it("Advent's own anchor Sunday is already week 1, not a separate anchor-week case", () => {
@@ -50,8 +62,15 @@ describe('getDayLabel — ordinal temporal label', () => {
     // reference engine, which shows the same pairing), so the label
     // reflects both, feast name first, same pattern as Trinity Sunday's
     // own St. Felix I case above.
-    expect(getDayLabel(resolveDay('2025-11-30'))).toBe('St. Andrew, Apostle — The 1st Sunday of Advent (Semiduplex)');
-    expect(getDayLabel(resolveDay('2025-12-01'))).toBe('Monday in the 1st week of Advent (Feria)');
+    expect(getDayLabel(resolveDay('2025-11-30')).en).toBe('St. Andrew, Apostle — The 1st Sunday of Advent (Semiduplex)');
+    // Advent drops the redundant leading weekday word now that the header
+    // always shows the weekday on its own (see temporalLabel's
+    // `dropWeekdayPrefix`).
+    expect(getDayLabel(resolveDay('2025-12-01')).en).toBe('In the 1st week of Advent (Feria)');
+    // Latin: same weekday-drop, and the season-ordinal genitive
+    // construction ("Hebdomada prima Adventus") needs no extra linking
+    // word — 4th-declension "Adventus" has the same genitive form.
+    expect(getDayLabel(resolveDay('2025-12-01')).la).toBe('In hebdomada prima Adventus (Feria)');
   });
 
   it('falls back to weekday + season name for seasons with no ordinal convention modeled', () => {
@@ -59,7 +78,7 @@ describe('getDayLabel — ordinal temporal label', () => {
     // (Duplex, added per the full-year sanctoral import) -- moved to
     // May 21, still within Ascensiontide 2026 (May 14-23) and still
     // free of any sanctoral entry.
-    expect(getDayLabel(resolveDay('2026-05-21'))).toContain('in Ascensiontide');
+    expect(getDayLabel(resolveDay('2026-05-21')).en).toContain('in Ascensiontide');
   });
 });
 
@@ -77,7 +96,7 @@ describe('getDayLabel — resumed post-Epiphany Sunday (overflow years)', () =>
     // Simplex commemoration (Ss. Tryphon, Respicius, and Nympha), shown
     // appended to the Sunday's own label per this app's usual
     // commemorated-Simplex display.
-    expect(getDayLabel(resolveDay('2024-11-10'))).toBe(
+    expect(getDayLabel(resolveDay('2024-11-10')).en).toBe(
       'Ss. Tryphon, Respicius, and Nympha, Martyrs — The 5th Sunday after Epiphany (Semiduplex)',
     );
     // 2024-11-11 is St. Martin of Tours (Duplex, pre-existing content) --
@@ -89,10 +108,10 @@ describe('getDayLabel — resumed post-Epiphany Sunday (overflow years)', () =>
     // overflow-week Monday instead (no single Nov-dated Monday near this
     // Sunday pair is clean any more, now that Nov 4/8/15/16/20 are all
     // fixed real content).
-    expect(getDayLabel(resolveDay('2024-11-11'))).toBe(
+    expect(getDayLabel(resolveDay('2024-11-11')).en).toBe(
       'St. Martin of Tours, Bishop and Confessor (Duplex Majus) — St. Menna, Martyr',
     );
-    expect(getDayLabel(resolveDay('2024-11-17'))).toBe('The 6th Sunday after Epiphany (Semiduplex)');
+    expect(getDayLabel(resolveDay('2024-11-17')).en).toBe('The 6th Sunday after Epiphany (Semiduplex)');
     // 2024-11-18 is the Dedication of the Basilicas of Ss. Peter and Paul
     // (pre-existing fixed content) -- again a real winning saint, not the
     // ferial fallback -- with St. Gregory Thaumaturgus (Semiduplex,
@@ -100,14 +119,14 @@ describe('getDayLabel — resumed post-Epiphany Sunday (overflow years)', () =>
     // direct instruction, a Semiduplex feast on an ordinary Sunday
     // transfers to the next open day rather than being commemorated in
     // place, and Nov 18 is that day.
-    expect(getDayLabel(resolveDay('2024-11-18'))).toBe(
+    expect(getDayLabel(resolveDay('2024-11-18')).en).toBe(
       'Dedication of the Basilicas of Ss. Peter and Paul (Duplex) — St. Gregory Thaumaturgus, Bishop and Confessor',
     );
     // 2035-10-29, a Monday in the 3rd week of a different overflow
     // stretch, is genuinely clean (no sanctoral entry, no commemoration)
     // -- covers the ferial "Monday in the Nth week after Epiphany" format
     // itself, independent of the specific 5th/6th Sunday pair above.
-    expect(getDayLabel(resolveDay('2035-10-29'))).toBe('Monday in the 3rd week after Epiphany (Feria)');
+    expect(getDayLabel(resolveDay('2035-10-29')).en).toBe('Monday in the 3rd week after Epiphany (Feria)');
   });
 
   it('the fixed final Sunday of the year always shows the fixed 23rd-after-Trinity ordinal, not a raw elapsed-week count', () => {
@@ -122,8 +141,8 @@ describe('getDayLabel — resumed post-Epiphany Sunday (overflow years)', () =>
     // Thaumaturgus above -- landing on 2026-11-23 instead, where St.
     // Clement already natively wins; Cecilia loses that tied collision
     // (both Semiduplex) and joins St. Felicitas as a commemoration there.
-    expect(getDayLabel(resolveDay('2026-11-22'))).toBe('The 23rd Sunday after Trinity (Semiduplex)');
-    expect(getDayLabel(resolveDay('2026-11-23'))).toBe(
+    expect(getDayLabel(resolveDay('2026-11-22')).en).toBe('The 23rd Sunday after Trinity (Semiduplex)');
+    expect(getDayLabel(resolveDay('2026-11-23')).en).toBe(
       'St. Clement I, Pope and Martyr (Semiduplex) — St. Felicitas, Martyr — St. Cecilia, Virgin and Martyr',
     );
     // 1943-11-21 is also the Presentation of the BVM (Duplex Majus, added
@@ -136,7 +155,7 @@ describe('getDayLabel — resumed post-Epiphany Sunday (overflow years)', () =>
     // additionally confirms the displaced Sunday is still commemorated in
     // return, using the same fixed 23rd-after-Trinity ordinal, not a raw
     // elapsed-week count recomputed for 1943.
-    expect(getDayLabel(resolveDay('1943-11-21'))).toBe(
+    expect(getDayLabel(resolveDay('1943-11-21')).en).toBe(
       'The Presentation of the Blessed Virgin Mary (Duplex Majus) — The 23rd Sunday after Trinity',
     );
   });
@@ -150,8 +169,10 @@ describe('getDayLabel — commemorated Sunday/feria under a sanctoral winner', (
     // (`decideOccurrence`'s `privileged-feria-minor` branch) -- live-
     // verified shape, same mechanism as the ordinary-Sunday case above,
     // for the feria-tier branch instead.
-    expect(getDayLabel(resolveDay('2027-12-07'))).toBe(
-      'St. Ambrose, Bishop, Confessor and Doctor of the Church (Duplex) — Tuesday in the 2nd week of Advent',
+    // Advent drops the redundant leading weekday word (see the Dec 1 case
+    // above).
+    expect(getDayLabel(resolveDay('2027-12-07')).en).toBe(
+      'St. Ambrose, Bishop, Confessor and Doctor of the Church (Duplex) — In the 2nd week of Advent',
     );
   });
 });
@@ -162,7 +183,7 @@ describe('getDayLabel — active octave', () => {
     // Clare's own day -- Simplex, below the octave's semiduplex threshold,
     // so she's commemorated rather than winning. Matches the live engine's
     // own title for this date directly (see saints/st-clare.yml).
-    expect(getDayLabel(resolveDay('2026-08-12'))).toBe(
+    expect(getDayLabel(resolveDay('2026-08-12')).en).toBe(
       '3rd Day within the Octave of St. Lawrence, Martyr (Semiduplex) — St. Clare, Virgin',
     );
   });
@@ -181,7 +202,7 @@ describe('getDayLabel — active octave', () => {
     // "real content closed the gap" shape as August's Lawrence/Assumption
     // overlap. Day 3 of the same octave (2028-11-03, a Friday) is still
     // genuinely open -- no sanctoral entry, no separate commemoration.
-    expect(getDayLabel(resolveDay('2028-11-03'))).toBe('3rd Day within the Octave of All Saints (Semiduplex)');
+    expect(getDayLabel(resolveDay('2028-11-03')).en).toBe('3rd Day within the Octave of All Saints (Semiduplex)');
   });
 
   it("a season's own named anchor day outranks an active octave, even though Trinity Sunday is technically also day 8 of Pentecost's own octave", () => {
@@ -191,14 +212,14 @@ describe('getDayLabel — active octave', () => {
     // muddy this specifically octave-vs-anchor-day check with a sanctoral
     // winner. 2030's Trinity Sunday (June 16) has no sanctoral entry at
     // all, isolating the octave interaction cleanly.
-    expect(getDayLabel(resolveDay('2030-06-16'))).toBe('Trinity Sunday (Duplex I Class)');
+    expect(getDayLabel(resolveDay('2030-06-16')).en).toBe('Trinity Sunday (Duplex I Class)');
   });
 
   it("a temporal day with real standing of its own (not ordinary-feria) never shows an octave name at all, even with one active -- live-verified counterexample: the Christmas Octave's own stack (Dec 30) titles itself off the Sunday, never any of the four octaves layered on top of it", () => {
     const day = resolveDay('2033-12-30');
     expect(day.temporalCategory).toBe('privileged-feria-minor');
-    expect(getDayLabel(day)).not.toContain('Octave');
-    expect(getDayLabel(day)).toBe('Friday in Christmastide (Feria)');
+    expect(getDayLabel(day).en).not.toContain('Octave');
+    expect(getDayLabel(day).en).toBe('Friday in Christmastide (Feria)');
   });
 
   it("picks the higher-ranked of two genuinely overlapping octaves for the label -- St. Lawrence's own elevated closing day (Aug 17) over the Assumption's ordinary day 3, even though the Assumption's octave started later and the Assumption is the higher-ranked feast overall -- with St. Hyacinth (Duplex, tied with Lawrence's own elevated rank) commemorated rather than winning outright", () => {
@@ -221,10 +242,10 @@ describe('getDayLabel — active octave', () => {
     // question): "Commemoratio: Tertia die infra Octavam S. Assumptionis
     // Beatæ Mariæ Virginis", not a bare "The Assumption of the Blessed
     // Virgin Mary".
-    expect(getDayLabel(resolveDay('2026-08-17'))).toBe(
+    expect(getDayLabel(resolveDay('2026-08-17')).en).toBe(
       'Octave of St. Lawrence, Martyr (Duplex) — 3rd Day within the Octave of The Assumption of the Blessed Virgin Mary — St. Hyacinth, Confessor',
     );
-    expect(getDayLabel(resolveDay('2026-08-18'))).toBe(
+    expect(getDayLabel(resolveDay('2026-08-18')).en).toBe(
       '4th Day within the Octave of The Assumption of the Blessed Virgin Mary (Semiduplex)',
     );
   });
@@ -243,10 +264,10 @@ describe('getDayLabel — active octave', () => {
     // octave mentions alongside a sanctoral winner.
     const day = resolveDay('2026-08-16');
     expect(day.weekday).toBe('sunday');
-    expect(getDayLabel(day)).toBe(
+    expect(getDayLabel(day).en).toBe(
       'St. Joachim, Confessor, Father of the Blessed Virgin Mary (Duplex II Class) — The 11th Sunday after Trinity',
     );
-    expect(getDayLabel(day)).not.toContain('Octave');
+    expect(getDayLabel(day).en).not.toContain('Octave');
   });
 
   it("a foreign octave superimposed on a privileged season still governs the label when its own effective rank clears that season's real threshold, with the season's own losing saint commemorated alongside it", () => {
@@ -266,7 +287,7 @@ describe('getDayLabel — active octave', () => {
     // mechanism (also used by hours/resolve-common.ts's
     // resolveOfficeWinner for the actual office content, not just this
     // label).
-    expect(getDayLabel(resolveDay('2026-12-15'))).toBe(
+    expect(getDayLabel(resolveDay('2026-12-15')).en).toBe(
       'Octave of The Immaculate Conception of the Blessed Virgin Mary (Duplex) — St. Eusebius of Vercelli, Bishop and Martyr',
     );
   });
@@ -280,7 +301,7 @@ describe('getDayLabel — active octave', () => {
     const day = resolveDay('2033-12-30');
     expect(day.temporalCategory).toBe('privileged-feria-minor');
     expect(day.season).toBe('christmastide');
-    expect(getDayLabel(day)).not.toContain('Octave');
+    expect(getDayLabel(day).en).not.toContain('Octave');
   });
 
   it('a sanctoral winner that outright displaces the only active octave still shows that octave with its full "Nth Day within the Octave" phrasing, not a bare feast name -- and without a rank, since the octave is riding along under the winning duplex rather than asserting its own rank', () => {
@@ -296,7 +317,7 @@ describe('getDayLabel — active octave', () => {
     // itself is what's being commemorated against a winning saint) and
     // also not `octaveLabel`'s own rank parenthetical (that belongs only
     // to an octave day when it's the day's own primary winner).
-    expect(getDayLabel(resolveDay('2026-08-19'))).toBe(
+    expect(getDayLabel(resolveDay('2026-08-19')).en).toBe(
       'St. John Eudes, Confessor (Duplex) — 5th Day within the Octave of The Assumption of the Blessed Virgin Mary',
     );
   });
@@ -311,7 +332,7 @@ describe('getDayLabel — named temporal feast rank', () => {
     // direct winner id) out of scope here. Pentecost Sunday's own id
     // *does* resolve as the direct winner (`temporal-id.ts`'s
     // EASTER_OFFSET_IDS), so it's a real, clean case for this branch.
-    expect(getDayLabel(resolveDay('2026-05-24'))).toBe('Pentecost (Duplex I Class)');
+    expect(getDayLabel(resolveDay('2026-05-24')).en).toBe('Pentecost (Duplex I Class)');
   });
 });
 
@@ -330,7 +351,7 @@ describe('getDayLabel — feast name combination', () => {
       ...base,
       winner: { kind: 'sanctoral', id: 'x', name: 'St. Ereden', rank: 'duplex' },
     };
-    expect(getDayLabel(day)).toBe('St. Ereden (Duplex)');
+    expect(getDayLabel(day).en).toBe('St. Ereden (Duplex)');
   });
 
   it('shows both, feast first, when the feast is merely commemorated', () => {
@@ -338,10 +359,10 @@ describe('getDayLabel — feast name combination', () => {
       ...base,
       commemorations: [{ kind: 'sanctoral', id: 'x', name: 'St. Ereden', rank: 'duplex-2-classis' }],
     };
-    expect(getDayLabel(day)).toBe('St. Ereden — Monday in the 2nd week after Trinity (Feria)');
+    expect(getDayLabel(day).en).toBe('St. Ereden — Monday in the 2nd week after Trinity (Feria)');
   });
 
   it('shows just the temporal label when nothing is commemorated at all', () => {
-    expect(getDayLabel(base)).toBe('Monday in the 2nd week after Trinity (Feria)');
+    expect(getDayLabel(base).en).toBe('Monday in the 2nd week after Trinity (Feria)');
   });
 });

tests/calendar/marian-saturday.test.ts

@@ -17,7 +17,7 @@ describe('Marian Saturday (applyMarianSaturday)', () => {
     const day = resolveDay('2026-07-04');
     expect(day.winner).toEqual({ kind: 'temporal', id: 'marian-saturday' });
     expect(day.commemorations).toEqual([]);
-    expect(getDayLabel(day)).toBe("Our Lady's Saturday (Simplex)");
+    expect(getDayLabel(day).en).toBe("Our Lady's Saturday (Simplex)");
   });
 
   it('wins over a Simplex saint, who is commemorated instead of winning outright', () => {

tests/hours/compline.test.ts

@@ -97,7 +97,7 @@ describe('resolveOrdo("compline", ...)', () => {
     const eve = resolveOrdo('compline', '2025-11-29');
     const last = eve.parts[eve.parts.length - 1];
     expect(last?.kind === 'preces' ? last.label : undefined).toBe('Alma Redemptoris Mater');
-    expect(eve.dayLabel).toBe('St. Andrew, Apostle — The 1st Sunday of Advent (Semiduplex)');
+    expect(eve.dayLabel?.en).toBe('St. Andrew, Apostle — The 1st Sunday of Advent (Semiduplex)');
 
     const dayBefore = resolveOrdo('compline', '2025-11-28');
     const lastBefore = dayBefore.parts[dayBefore.parts.length - 1];

tests/ui/shell.test.ts

@@ -19,6 +19,10 @@ describe('shell', () => {
     mountShell(root);
 
     expect(root.querySelector('.day-nav-date')?.textContent).toContain('August 9, 2026');
+    // The "day being celebrated" text now lives in the merged day-nav
+    // header, not repeated inside each hour's own view.
+    expect(root.querySelector('.day-nav-label')?.textContent).toBeTruthy();
+    expect(root.querySelector('.hour-view .day-label')).toBeNull();
 
     const hourNames = Array.from(root.querySelectorAll('.hour-name')).map((el) => el.textContent);
     expect(hourNames).toEqual([