fix(locale): localize ISO 8601 calendar weekday/month names (#8987) (#9013)

* docs(plugins): add microsoft 365 calendar provider plan

* docs(plugins): add microsoft 365 calendar provider plan

* docs(ios): plan internal testflight builds

* fix(locale): localize ISO calendar weekday/month names (#8987)

PR #8991 localized ISO 8601 weekday labels only in the custom
Schedule/Habits/Planner components. Material <mat-calendar> (schedule-task
dialog, deadline dialog, date-picker inputs, repeat-task heatmap) still
rendered month + weekday names via the global adapter locale 'sv' (the ISO
sentinel), so they showed Swedish and ignored the app language.

Override getDayOfWeekNames, getMonthNames and the spelled-out branch of
format() in CustomDateAdapter to run under a temporary swap to
isoTextLocale() (the UI language) when the ISO option is active. Numeric
dateInput and time-only formats keep the configured locale, so ISO stays
YYYY-MM-DD and the 24h clock is preserved. The swap assigns this.locale
directly (not setLocale) so it fires no spurious localeChanges.

Add unit coverage for the adapter and a real <mat-calendar> integration
spec asserting UI-language headers, a live language switch, and the
non-ISO fallback.

src/app/core/date-time-format/custom-date-adapter.calendar.spec.ts

@@ -0,0 +1,109 @@
+import { Component } from '@angular/core';
+import { ComponentFixture, TestBed } from '@angular/core/testing';
+import { NoopAnimationsModule } from '@angular/platform-browser/animations';
+import {
+  DateAdapter,
+  MAT_DATE_FORMATS,
+  MAT_DATE_LOCALE,
+  MAT_NATIVE_DATE_FORMATS,
+} from '@angular/material/core';
+import { MatDatepickerModule } from '@angular/material/datepicker';
+import { CustomDateAdapter } from './custom-date-adapter';
+import { DateTimeFormatService } from './date-time-format.service';
+import { GlobalConfigService } from '../../features/config/global-config.service';
+
+/**
+ * Integration coverage for the #8987 follow-up: the Material `<mat-calendar>`
+ * (used by the schedule-task dialog, deadline dialog, etc.) must render its
+ * weekday header in the UI language when the ISO 8601 option is active, and
+ * update live when the language changes — while the adapter locale itself stays
+ * `sv` (the ISO sentinel).
+ */
+@Component({
+  standalone: true,
+  imports: [MatDatepickerModule],
+  template: `<mat-calendar [startAt]="startAt"></mat-calendar>`,
+})
+class CalendarHostComponent {
+  startAt = new Date(2026, 6, 14);
+}
+
+describe('CustomDateAdapter × mat-calendar weekday header', () => {
+  let fixture: ComponentFixture<CalendarHostComponent>;
+  let adapter: DateAdapter<Date>;
+  let isoTextLocale: string | null;
+
+  const longWeekdayNames = (): string[] => {
+    const host = fixture.nativeElement as HTMLElement;
+    return Array.from(
+      host.querySelectorAll<HTMLElement>(
+        '.mat-calendar-table-header th .cdk-visually-hidden',
+      ),
+      (el) => el.textContent?.trim() ?? '',
+    );
+  };
+
+  beforeEach(() => {
+    isoTextLocale = 'en';
+
+    const dateTimeFormatServiceMock: Partial<DateTimeFormatService> = {
+      isoTextLocale: (() => isoTextLocale) as DateTimeFormatService['isoTextLocale'],
+      dateFormat: (() => ({
+        raw: 'yyyy-MM-dd',
+        humanReadable: 'YYYY-MM-DD',
+      })) as DateTimeFormatService['dateFormat'],
+      formatDate: (date: Date) => date.toISOString().slice(0, 10),
+    };
+
+    TestBed.configureTestingModule({
+      imports: [CalendarHostComponent, NoopAnimationsModule],
+      providers: [
+        { provide: DateAdapter, useClass: CustomDateAdapter },
+        { provide: MAT_DATE_LOCALE, useValue: 'sv' },
+        { provide: MAT_DATE_FORMATS, useValue: MAT_NATIVE_DATE_FORMATS },
+        { provide: DateTimeFormatService, useValue: dateTimeFormatServiceMock },
+        {
+          provide: GlobalConfigService,
+          useValue: { localization: () => ({ firstDayOfWeek: 1 }) },
+        },
+      ],
+    });
+
+    adapter = TestBed.inject(DateAdapter);
+    // Mirror the running app: the ISO 8601 option keeps `sv` as the adapter locale.
+    adapter.setLocale('sv');
+
+    fixture = TestBed.createComponent(CalendarHostComponent);
+    fixture.detectChanges();
+  });
+
+  it('renders the weekday header in the UI language, not Swedish', () => {
+    const names = longWeekdayNames();
+    expect(names).toContain('Monday');
+    expect(names).not.toContain('måndag');
+    // Adapter locale is untouched, so numeric/date formatting stays ISO.
+    expect((adapter as unknown as { locale: string }).locale).toBe('sv');
+  });
+
+  it('updates the header live when the UI language changes', () => {
+    expect(longWeekdayNames()).toContain('Monday');
+
+    // Simulate a language switch: the service effect re-applies the adapter
+    // locale, whose localeChanges event makes the calendar re-read the names.
+    isoTextLocale = 'de';
+    adapter.setLocale('sv');
+    fixture.detectChanges();
+
+    const names = longWeekdayNames();
+    expect(names).toContain('Montag');
+    expect(names).not.toContain('Monday');
+  });
+
+  it('falls back to the adapter locale for non-ISO options (null text locale)', () => {
+    isoTextLocale = null;
+    adapter.setLocale('sv');
+    fixture.detectChanges();
+
+    expect(longWeekdayNames()).toContain('måndag');
+  });
+});

src/app/core/date-time-format/custom-date-adapter.spec.ts

@@ -0,0 +1,111 @@
+import { TestBed } from '@angular/core/testing';
+import { MAT_DATE_LOCALE } from '@angular/material/core';
+import { CustomDateAdapter } from './custom-date-adapter';
+import { DateTimeFormatService } from './date-time-format.service';
+import { GlobalConfigService } from '../../features/config/global-config.service';
+
+describe('CustomDateAdapter (ISO weekday/month localization)', () => {
+  let adapter: CustomDateAdapter;
+  let isoTextLocale: string | null;
+
+  const RAW_NUMERIC_FORMAT = 'yyyy-MM-dd';
+  const NUMERIC_SENTINEL = 'NUMERIC-2026-07-14';
+  // July 14, 2026 (month index 6). Local components are UTC-normalized by the
+  // adapter's `_format`, so the rendered month/weekday is stable across zones.
+  const testDate = new Date(2026, 6, 14);
+
+  beforeEach(() => {
+    isoTextLocale = null;
+
+    const dateTimeFormatServiceMock: Partial<DateTimeFormatService> = {
+      isoTextLocale: (() => isoTextLocale) as DateTimeFormatService['isoTextLocale'],
+      dateFormat: (() => ({
+        raw: RAW_NUMERIC_FORMAT,
+        humanReadable: RAW_NUMERIC_FORMAT.toUpperCase(),
+      })) as DateTimeFormatService['dateFormat'],
+      formatDate: () => NUMERIC_SENTINEL,
+    };
+
+    TestBed.configureTestingModule({
+      providers: [
+        CustomDateAdapter,
+        { provide: MAT_DATE_LOCALE, useValue: 'sv' },
+        { provide: DateTimeFormatService, useValue: dateTimeFormatServiceMock },
+        {
+          provide: GlobalConfigService,
+          useValue: { localization: () => ({ firstDayOfWeek: 1 }) },
+        },
+      ],
+    });
+
+    adapter = TestBed.inject(CustomDateAdapter);
+    // Mirror the app: the ISO 8601 option keeps `sv` as the adapter locale.
+    adapter.setLocale('sv');
+  });
+
+  describe('with an ISO text locale set (ISO 8601 option active)', () => {
+    it('renders weekday names in the UI language', () => {
+      isoTextLocale = 'en';
+      expect(adapter.getDayOfWeekNames('long')).toContain('Monday');
+
+      isoTextLocale = 'de';
+      expect(adapter.getDayOfWeekNames('long')).toContain('Montag');
+    });
+
+    it('renders month names in the UI language', () => {
+      isoTextLocale = 'en';
+      expect(adapter.getMonthNames('long')[6]).toBe('July');
+
+      isoTextLocale = 'de';
+      expect(adapter.getMonthNames('long')[6]).toBe('Juli');
+    });
+
+    it('renders the spelled-out month/year header in the UI language', () => {
+      isoTextLocale = 'en';
+      expect(adapter.format(testDate, { year: 'numeric', month: 'long' })).toBe(
+        'July 2026',
+      );
+    });
+
+    it('keeps the numeric date format on the configured locale', () => {
+      isoTextLocale = 'en';
+      expect(adapter.format(testDate, RAW_NUMERIC_FORMAT)).toBe(NUMERIC_SENTINEL);
+    });
+
+    it('keeps time-only formats on the adapter locale (24h preserved)', () => {
+      isoTextLocale = 'en-US';
+      const withTime = new Date(2026, 6, 14, 13, 0, 0);
+      expect(adapter.format(withTime, { hour: 'numeric', minute: '2-digit' })).toBe(
+        '13:00',
+      );
+    });
+
+    it('restores the adapter locale after a localized read', () => {
+      isoTextLocale = 'de';
+      adapter.getMonthNames('long');
+      adapter.getDayOfWeekNames('narrow');
+      adapter.format(testDate, { year: 'numeric', month: 'long' });
+
+      expect((adapter as unknown as { locale: string }).locale).toBe('sv');
+    });
+  });
+
+  describe('without an ISO text locale (every non-ISO option)', () => {
+    it('leaves weekday names on the adapter locale', () => {
+      isoTextLocale = null;
+      expect(adapter.getDayOfWeekNames('long')).toContain('måndag');
+    });
+
+    it('leaves month names on the adapter locale', () => {
+      isoTextLocale = null;
+      expect(adapter.getMonthNames('long')[6]).toBe('juli');
+    });
+
+    it('leaves the month/year header on the adapter locale', () => {
+      isoTextLocale = null;
+      expect(adapter.format(testDate, { year: 'numeric', month: 'long' })).toBe(
+        'juli 2026',
+      );
+    });
+  });
+});

src/app/core/date-time-format/custom-date-adapter.ts

@@ -52,7 +52,57 @@ export class CustomDateAdapter extends NativeDateAdapter {
       return this._dateTimeFormatService.formatDate(date);
     }
 
+    // Spelled-out month/weekday labels (e.g. the calendar's "July 2026" header)
+    // follow the UI language when the ISO 8601 option is active. Numeric and
+    // time-only formats keep the configured locale, so ISO stays YYYY-MM-DD and
+    // the 24h clock is preserved (#8987 follow-up).
+    if (this._hasSpelledOutName(displayFormat)) {
+      return this._withTextLocale(() => super.format(date, displayFormat));
+    }
+
     // For other formats, use default
     return super.format(date, displayFormat);
   }
+
+  // Calendar weekday header row ('M T W ...'). Localized to the UI language for
+  // the ISO 8601 option; unchanged for every other locale.
+  override getDayOfWeekNames(style: 'long' | 'short' | 'narrow'): string[] {
+    return this._withTextLocale(() => super.getDayOfWeekNames(style));
+  }
+
+  // Month names shown in the calendar's year view.
+  override getMonthNames(style: 'long' | 'short' | 'narrow'): string[] {
+    return this._withTextLocale(() => super.getMonthNames(style));
+  }
+
+  /**
+   * Run `fn` with the adapter locale temporarily swapped to the ISO text locale
+   * (the UI language, exposed only when the ISO 8601 option is selected). When
+   * no ISO text locale is set the callback runs unchanged. Direct field
+   * assignment is used instead of `setLocale()` so no `localeChanges` event
+   * fires during the swap.
+   */
+  private _withTextLocale<T>(fn: () => T): T {
+    const textLocale = this._dateTimeFormatService.isoTextLocale();
+    if (!textLocale) return fn();
+
+    const prevLocale = this.locale;
+    this.locale = textLocale;
+    try {
+      return fn();
+    } finally {
+      this.locale = prevLocale;
+    }
+  }
+
+  private _hasSpelledOutName(
+    displayFormat: Intl.DateTimeFormatOptions | string,
+  ): boolean {
+    if (typeof displayFormat === 'string') return false;
+    const spelledOut = ['long', 'short', 'narrow'];
+    return (
+      spelledOut.includes(displayFormat.weekday as string) ||
+      spelledOut.includes(displayFormat.month as string)
+    );
+  }
 }