fix: write calendar dates in the order of the app language

src/components/calendar/EventModal.tsx

@@ -47,6 +47,7 @@ import { editorTimesFromEvent, eventTimeFieldsToSave } from '../../lib/event-edi
 import { useSettingsStore } from '../../stores/settings-store';
 import { canCreateEventsIn } from '../../lib/calendar-editability';
 import { useCalendarLocale } from '../../lib/calendar-locale';
+import { formatCalendarDate } from '../../lib/date-format';
 import {
   alertsToReminders,
   remindersToAlerts,
@@ -530,7 +531,7 @@ export function EventModal({
                   style={styles.dateBtn}
                   onPress={() => setShowStartDate(true)}
                 >
-                  <Text style={styles.dateText}>{format(start, 'EEE, MMM d', { locale })}</Text>
+                  <Text style={styles.dateText}>{formatCalendarDate(start, locale.code, 'weekdayMonthDay')}</Text>
                 </Pressable>
                 {!allDay && (
                   <Pressable
@@ -550,7 +551,7 @@ export function EventModal({
                   style={styles.dateBtn}
                   onPress={() => setShowEndDate(true)}
                 >
-                  <Text style={styles.dateText}>{format(end, 'EEE, MMM d', { locale })}</Text>
+                  <Text style={styles.dateText}>{formatCalendarDate(end, locale.code, 'weekdayMonthDay')}</Text>
                 </Pressable>
                 {!allDay && (
                   <Pressable

src/lib/__tests__/calendar-date-format.test.ts

@@ -0,0 +1,21 @@
+import { describe, expect, it } from 'vitest';
+import { formatCalendarDate } from '../date-format';
+
+const oct15 = new Date(2026, 9, 15, 10, 0);
+
+describe('formatCalendarDate', () => {
+  it('puts the day before the month in German', () => {
+    const s = formatCalendarDate(oct15, 'de', 'weekdayMonthDay');
+    expect(s).toMatch(/15\. Okt/);
+    expect(s).not.toMatch(/Okt\.? 15/);
+  });
+
+  it('keeps the US order in English', () => {
+    expect(formatCalendarDate(oct15, 'en-US', 'weekdayMonthDay')).toBe('Thu, Oct 15');
+    expect(formatCalendarDate(oct15, 'en', 'monthDayYear')).toBe('Oct 15, 2026');
+  });
+
+  it('names the weekday in full with the year for an all-day date', () => {
+    expect(formatCalendarDate(oct15, 'de', 'longWeekdayMonthDayYear')).toMatch(/^Donnerstag, 15\. Okt\.? 2026$/);
+  });
+});

src/lib/date-format.ts

@@ -17,7 +17,8 @@ import type { DateFormat, TimeFormat } from '../stores/settings-store';
 type Translate = (key: string, fallback?: string, params?: Record<string, string | number>) => string;
 
 type FormatName =
-  | 'time12' | 'time24' | 'full12' | 'full24' | 'weekday' | 'date' | 'monthDay' | 'monthDayYear';
+  | 'time12' | 'time24' | 'full12' | 'full24' | 'weekday' | 'date' | 'monthDay' | 'monthDayYear'
+  | 'weekdayMonthDay' | 'longWeekdayMonthDayYear';
 
 const FORMATS: Record<FormatName, Intl.DateTimeFormatOptions> = {
   time12: { hour: '2-digit', minute: '2-digit', hour12: true },
@@ -28,6 +29,8 @@ const FORMATS: Record<FormatName, Intl.DateTimeFormatOptions> = {
   date: { year: 'numeric', month: '2-digit', day: '2-digit' },
   monthDay: { month: 'short', day: 'numeric' },
   monthDayYear: { month: 'short', day: 'numeric', year: 'numeric' },
+  weekdayMonthDay: { weekday: 'short', month: 'short', day: 'numeric' },
+  longWeekdayMonthDayYear: { weekday: 'long', month: 'short', day: 'numeric', year: 'numeric' },
 };
 
 // Building an Intl formatter is the expensive part of formatting a date (on
@@ -124,3 +127,17 @@ export function formatListDate(
 
   return formatWith(d, intlLocale, 'date');
 }
+
+export type CalendarDateStyle = 'weekdayMonthDay' | 'longWeekdayMonthDayYear' | 'monthDay' | 'monthDayYear';
+
+/**
+ * A calendar date in the order and words of `locale` ("Thu, Oct 15",
+ * "Do., 15. Okt."). The calendar used fixed US patterns such as
+ * 'EEE, MMM d', which put German and most other languages in the wrong order.
+ * `locale` is a language tag such as a date-fns locale's `code`.
+ */
+export function formatCalendarDate(date: Date, locale: string | undefined, style: CalendarDateStyle): string {
+  syncFormatterZone(new Date());
+  const tag = !locale || locale === 'en' ? 'en-US' : locale;
+  return formatWith(date, tag, style);
+}