Give every locale its own strings on the non-prompt surfaces

Four locales received English on surfaces whose translations were
already complete, because the resolving code was a de/en binary.

- Medication reminder push and the Telegram inline-keyboard labels
  admitted only de/en, so es/fr/it/pl got the English template on every
  channel. Route the resolver through a shared coerceLocale().
- The Coach's trailing "reply now in X" clause said English for any
  non-German locale, overriding the correct system-prompt directive.
  Read the language name from a shared map instead.
- Coach refusal copy was a de/en constant pair, answering four locales
  in English at the one turn the Coach is declining to help. Move the
  copy into the bundles; the EN/DE constants now derive from them.
- The sleep-stage chart formatted axis ticks as en-US for four locales;
  the cycle calendar and the device-score tile followed the *browser*
  locale rather than the app locale.
- Three components carried a byte-identical duration formatter that
  branched on German. Lift it to one key-driven helper.

Polish needs a third plural tier: 2-4 takes a "few" form a two-form
scheme cannot express, so "2 godzin temu" read as "2 of-hours ago".
Add a pluralKey() helper driven by Intl.PluralRules and a Few tier to
the relative-time and stale-hint keys. The five locales whose rules
have no "few" category resolve exactly as before by construction, and
their Few values mirror Other. Teach the reverse-coverage guard to
expand a pluralKey() base into its three tiers.

src/components/charts/trend-card.tsx

@@ -10,6 +10,7 @@ import {
   TooltipTrigger,
 } from "@/components/ui/tooltip";
 import { useTranslations, useFormatters } from "@/lib/i18n/context";
+import { pluralKey } from "@/lib/i18n/plural";
 import type { ComparisonBaseline } from "@/lib/dashboard-layout";
 import {
   getTrendSentiment,
@@ -130,7 +131,7 @@ export function TrendCard({
   emptyHint = null,
   valueAdornment = null,
 }: TrendCardProps) {
-  const { t } = useTranslations();
+  const { t, locale } = useTranslations();
   const fmt = useFormatters();
 
   // v1.4.33 F5 — pick a single signal to drive both the arrow and the
@@ -370,20 +371,14 @@ export function TrendCard({
               }
               if (staleDays <= 60) {
                 const weeks = Math.floor(staleDays / 7);
-                return t(
-                  weeks === 1
-                    ? "dashboard.staleHintWeeksOne"
-                    : "dashboard.staleHintWeeksOther",
-                  { count: weeks },
-                );
+                return t(pluralKey("dashboard.staleHintWeeks", weeks, locale), {
+                  count: weeks,
+                });
               }
               const months = Math.floor(staleDays / 30);
-              return t(
-                months === 1
-                  ? "dashboard.staleHintMonthsOne"
-                  : "dashboard.staleHintMonthsOther",
-                { count: months },
-              );
+              return t(pluralKey("dashboard.staleHintMonths", months, locale), {
+                count: months,
+              });
             })()}
           </span>
         )}

src/components/cycle/cycle-calendar.tsx

@@ -6,6 +6,8 @@ import { ChevronLeft, ChevronRight } from "lucide-react";
 import { cn } from "@/lib/utils";
 import { Button } from "@/components/ui/button";
 import { useTranslations } from "@/lib/i18n/context";
+import { resolveIntlLocale } from "@/lib/format-locale";
+import type { Locale } from "@/lib/i18n/config";
 import type { CalendarDay } from "./types";
 import {
   FERTILE_HUE,
@@ -30,9 +32,17 @@ import {
  * grid is never colour-only. WCAG 2.5.5 — each cell is ≥ 40 px.
  */
 
-/** Monday-first short weekday labels, localized via Intl (no i18n key). */
-function shortWeekdays(): string[] {
-  const fmt = new Intl.DateTimeFormat(undefined, { weekday: "short" });
+/**
+ * Monday-first short weekday labels, localized via Intl (no i18n key).
+ *
+ * Takes the APP locale explicitly. It used to pass `undefined`, which resolves
+ * to the browser's locale — invisible whenever the two agree, and wrong for
+ * every user who reads the app in a language their browser is not set to.
+ */
+function shortWeekdays(locale: Locale): string[] {
+  const fmt = new Intl.DateTimeFormat(resolveIntlLocale(locale), {
+    weekday: "short",
+  });
   // 2024-01-01 is a Monday — walk 7 days for a Monday-first header row.
   return Array.from({ length: 7 }, (_, i) =>
     fmt.format(new Date(2024, 0, 1 + i)),
@@ -71,8 +81,8 @@ export function CycleCalendar({
   onSelectDay,
   className,
 }: CycleCalendarProps) {
-  const { t } = useTranslations();
-  const weekdays = useMemo(() => shortWeekdays(), []);
+  const { t, locale } = useTranslations();
+  const weekdays = useMemo(() => shortWeekdays(locale), [locale]);
   const byDate = useMemo(() => new Map(days.map((d) => [d.date, d])), [days]);
 
   // Anchor the visible month on today's month.
@@ -104,7 +114,7 @@ export function CycleCalendar({
     return cells;
   }, [monthAnchor]);
 
-  const monthLabel = monthAnchor.toLocaleDateString(undefined, {
+  const monthLabel = monthAnchor.toLocaleDateString(resolveIntlLocale(locale), {
     month: "long",
     year: "numeric",
   });

src/components/insights/coach-panel/history-rail.tsx

@@ -64,7 +64,7 @@ export function HistoryRail({
   className,
   hideHeading = false,
 }: HistoryRailProps) {
-  const { t } = useTranslations();
+  const { t, locale } = useTranslations();
   const [filter, setFilter] = useState<string>("");
   // v1.30.2 (QoL H1) — the search box now drives a SERVER-side query
   // (title-only substring, see the route doc comment), so debounce the
@@ -242,7 +242,7 @@ export function HistoryRail({
                     <span className="truncate">{c.title}</span>
                   </span>
                   <span className="text-muted-foreground block text-xs">
-                    {formatRelativeTime(c.updatedAt, t)}
+                    {formatRelativeTime(c.updatedAt, t, locale)}
                   </span>
                 </button>
                 {/* v1.4.27 R3d MB2 — drop the hover-only `opacity-0`

src/components/insights/device-score-tile.tsx

@@ -5,6 +5,7 @@ import type { ComponentType } from "react";
 import { useAuth } from "@/hooks/use-auth";
 import { useInsightsAnalytics } from "@/hooks/use-insights-analytics";
 import { useTranslations } from "@/lib/i18n/context";
+import { resolveIntlLocale } from "@/lib/format-locale";
 import type { DataSummary } from "@/lib/analytics/trends";
 import { Card, CardContent, CardHeader } from "@/components/ui/card";
 import { LearningGate } from "@/components/ui/learning-gate";
@@ -72,7 +73,7 @@ export function DeviceScoreTile({
   learningThreshold = 3,
   className,
 }: DeviceScoreTileProps) {
-  const { t } = useTranslations();
+  const { t, locale } = useTranslations();
   const { user } = useAuth();
 
   const count = summary?.count ?? 0;
@@ -83,7 +84,7 @@ export function DeviceScoreTile({
   const isLearning = count < learningThreshold;
 
   const fmt = (value: number) =>
-    value.toLocaleString(undefined, {
+    value.toLocaleString(resolveIntlLocale(locale), {
       minimumFractionDigits: fractionDigits,
       maximumFractionDigits: fractionDigits,
     });

src/components/insights/sleep-source-discrepancy-marker.tsx

@@ -9,6 +9,7 @@ import {
   TooltipTrigger,
 } from "@/components/ui/tooltip";
 import { useTranslations } from "@/lib/i18n/context";
+import { formatDurationMinutes } from "@/lib/i18n/duration";
 
 /**
  * v1.28.x — the discreet "sources disagree" marker, extracted from
@@ -29,15 +30,6 @@ export interface SleepSourceDiscrepancyDto {
   }[];
 }
 
-export function formatMinutes(total: number, locale: string): string {
-  const hours = Math.floor(total / 60);
-  const mins = Math.round(total - hours * 60);
-  if (locale === "de") {
-    return hours > 0 ? `${hours} Std. ${mins} Min.` : `${mins} Min.`;
-  }
-  return hours > 0 ? `${hours}h ${mins}m` : `${mins}m`;
-}
-
 /**
  * Localised label keys per `MeasurementSource` — the same map the
  * source-priority settings surface uses (`sources-section.tsx`), so both
@@ -110,7 +102,7 @@ export function SleepSourceDiscrepancyMarker({
   discrepancy,
   align = "start",
 }: SleepSourceDiscrepancyMarkerProps) {
-  const { t, locale } = useTranslations();
+  const { t } = useTranslations();
   if (!discrepancy) return null;
   return (
     <TooltipProvider delayDuration={150}>
@@ -137,7 +129,7 @@ export function SleepSourceDiscrepancyMarker({
             {discrepancy.sources
               .map(
                 (b) =>
-                  `${sourceDisplayName(b.source, b.deviceType, t)} ${formatMinutes(b.asleepMinutes, locale)}`,
+                  `${sourceDisplayName(b.source, b.deviceType, t)} ${formatDurationMinutes(b.asleepMinutes, t)}`,
               )
               .join(" · ")}
           </p>

src/components/insights/sleep-stage-stacked-bar.tsx

@@ -16,6 +16,9 @@ import {
 import { Button } from "@/components/ui/button";
 import { Card, CardContent, CardHeader, CardTitle } from "@/components/ui/card";
 import { useTranslations } from "@/lib/i18n/context";
+import { formatDurationMinutes } from "@/lib/i18n/duration";
+import { resolveIntlLocale } from "@/lib/format-locale";
+import type { Locale } from "@/lib/i18n/config";
 
 /**
  * v1.4.25 W4c → W3f — sleep-stage composition chart.
@@ -97,15 +100,6 @@ export const STAGE_COLORS: Record<string, string> = {
   IN_BED: "var(--chart-inbed)", // muted blue-grey — pre-asleep
 };
 
-function formatMinutes(total: number, locale: string): string {
-  const hours = Math.floor(total / 60);
-  const mins = Math.round(total - hours * 60);
-  if (locale === "de") {
-    return hours > 0 ? `${hours} Std. ${mins} Min.` : `${mins} Min.`;
-  }
-  return hours > 0 ? `${hours}h ${mins}m` : `${mins}m`;
-}
-
 /**
  * Format a Berlin-tz day key (YYYY-MM-DD) as a short x-axis tick.
  * 7-day window → "Mon" / "Tue" / …; 14-day → "M 10" / "T 11" / …;
@@ -123,13 +117,13 @@ function formatMinutes(total: number, locale: string): string {
 function formatDayTick(
   dayKey: string,
   window: WindowSize,
-  locale: string,
+  locale: Locale,
 ): string {
   const [y, m, d] = dayKey.split("-").map(Number);
   if (!y || !m || !d) return dayKey;
   const date = new Date(Date.UTC(y, m - 1, d));
   if (window === 7) {
-    return date.toLocaleDateString(locale === "de" ? "de-DE" : "en-US", {
+    return date.toLocaleDateString(resolveIntlLocale(locale), {
       timeZone: "UTC",
       weekday: "short",
     });
@@ -137,7 +131,7 @@ function formatDayTick(
   if (window === 14) {
     return `${date.getUTCDate()}.`;
   }
-  return date.toLocaleDateString(locale === "de" ? "de-DE" : "en-US", {
+  return date.toLocaleDateString(resolveIntlLocale(locale), {
     timeZone: "UTC",
     month: "short",
     day: "numeric",
@@ -322,7 +316,7 @@ export function SleepStageStackedBar({ breakdown }: SleepStageStackedBarProps) {
                                 {stageLabels[stage] ?? stage}
                               </span>
                               <span className="text-muted-foreground">
-                                {formatMinutes(minutes, locale)} · {pct}%
+                                {formatDurationMinutes(minutes, t)} · {pct}%
                               </span>
                             </div>
                           );
@@ -330,7 +324,7 @@ export function SleepStageStackedBar({ breakdown }: SleepStageStackedBarProps) {
                         {totalNight > 0 && (
                           <div className="border-border mt-1 flex items-center justify-between gap-3 border-t pt-1 font-medium">
                             <span>{t("insights.sleep.headlineTitle")}</span>
-                            <span>{formatMinutes(totalNight, locale)}</span>
+                            <span>{formatDurationMinutes(totalNight, t)}</span>
                           </div>
                         )}
                       </div>

src/components/measurements/measurement-list.tsx

@@ -100,6 +100,7 @@ import {
   INSIGHTS_OVERVIEW_PATH,
   subPageSlugForType,
 } from "@/lib/insights/sub-page-metric";
+import { formatDurationMinutes } from "@/lib/i18n/duration";
 
 /**
  * v1.4.37 W7c — cumulative HK types whose list view collapses to one
@@ -140,19 +141,6 @@ interface Measurement {
   awakenings?: number;
 }
 
-/**
- * v1.11.5 — format a minutes total as an "8h 12m" / "8 Std. 12 Min."
- * sleep headline.
- */
-function formatSleepMinutes(total: number, locale: string): string {
-  const hours = Math.floor(total / 60);
-  const mins = Math.round(total - hours * 60);
-  if (locale === "de") {
-    return hours > 0 ? `${hours} Std. ${mins} Min.` : `${mins} Min.`;
-  }
-  return hours > 0 ? `${hours}h ${mins}m` : `${mins}m`;
-}
-
 /** v1.11.5 — i18n labels for the sleep stages shown in the drill-down. */
 function sleepStageLabel(
   stage: string | null | undefined,
@@ -287,7 +275,7 @@ export function MeasurementList({
   lockedType,
   initialType,
 }: MeasurementListProps) {
-  const { t, locale } = useTranslations();
+  const { t } = useTranslations();
   const fmt = useFormatters();
   const { isAuthenticated } = useAuth();
   // v1.28.42 (H3) — the desktop table and the mobile card list used to BOTH
@@ -1023,7 +1011,7 @@ export function MeasurementList({
                                 TIME ASLEEP as "8h 12m" + a nap caption. */}
                               {isSleep ? (
                                 <>
-                                  {formatSleepMinutes(m.value, locale)}
+                                  {formatDurationMinutes(m.value, t)}
                                   <SleepNightCaption m={m} />
                                 </>
                               ) : (
@@ -1228,7 +1216,7 @@ export function MeasurementList({
                                 "78.4 kg" no longer truncates to "78".
                                 v1.11.5 — sleep rows render TIME ASLEEP. */}
                               {isSleep ? (
-                                formatSleepMinutes(m.value, locale)
+                                formatDurationMinutes(m.value, t)
                               ) : (
                                 <>
                                   {isGrouped
@@ -1590,7 +1578,7 @@ function DayDrillDown({
   unit: string;
   layout: "desktop" | "mobile";
 }) {
-  const { t, locale } = useTranslations();
+  const { t } = useTranslations();
   const { isAuthenticated } = useAuth();
   const { data, isLoading, error } = useQuery({
     queryKey: queryKeys.measurementDrilldown(type, dayKey),
@@ -1652,7 +1640,7 @@ function DayDrillDown({
             </span>
             <span className="font-medium tabular-nums">
               {isSleep
-                ? formatSleepMinutes(s.value, locale)
+                ? formatDurationMinutes(s.value, t)
                 : `${s.value} ${unit}`}
             </span>
           </div>
@@ -1673,9 +1661,7 @@ function DayDrillDown({
               : formatDateTime(s.measuredAt)}
           </span>
           <span className="font-medium tabular-nums">
-            {isSleep
-              ? formatSleepMinutes(s.value, locale)
-              : `${s.value} ${unit}`}
+            {isSleep ? formatDurationMinutes(s.value, t) : `${s.value} ${unit}`}
           </span>
         </div>
       ))}