fix(ui5-date-picker): prevent CLDR cache-poisoning and crash during language change

When setLanguage() is called without await, there is a race between the CLDR
fetch completing and re-renders still in the deferred render queue. A component
queued for rendering before the language change started would still call
onBeforeRendering / onAfterRendering with stale or missing locale data.

Two-layer fix:

1. UI5Element._render(): skip the render entirely for languageAware components
   while getLanguageChangePending() is non-null. _invalidate() already blocks
   new invalidations during this window, but components already in the render
   queue (queued before the language change fired) could still reach _render().
   This guard closes that gap — no lifecycle hooks are entered, and
   reRenderAllUI5Elements({ languageAware: true }) re-renders them once CLDR
   is ready.

2. getCachedLocaleDataInstance: attach attachLanguageChange(() => cache.clear())
   so any cached LocaleData instances are discarded when the language changes.
   This ensures the next call after CLDR loads gets a fresh, valid instance
   rather than a stale one built against the old locale data.

Fixes the TypeError: Cannot read properties of undefined (reading
'ca-gregorian') seen in DatePicker Cypress tests when setLanguage is called
without await.

Author: nnaydenow

packages/base/src/UI5Element.ts

@@ -898,6 +898,16 @@ abstract class UI5Element extends HTMLElement {
 	 */
 	_render() {
 		const ctor = this.constructor as typeof UI5Element;
+
+		// Skip rendering language-aware components while a language change (CLDR + i18n fetch) is
+		// still in flight. reRenderAllUI5Elements({ languageAware: true }) will re-render them once
+		// the data is ready. Without this guard, a component added to the render queue *before* the
+		// language change started (e.g. via renderDeferred) can still call onBeforeRendering and
+		// onAfterRendering with stale or missing locale data.
+		if (ctor.getMetadata().isLanguageAware() && getLanguageChangePending()) {
+			return;
+		}
+
 		const hasIndividualSlots = ctor.getMetadata().hasIndividualSlots();
 
 		// restore properties that were initialized before `define` by calling the setter

packages/localization/src/getCachedLocaleDataInstance.ts

@@ -16,17 +16,10 @@ attachLanguageChange(() => {
 });
 
 const getCachedLocaleDataInstance = (locale: Locale) => {
-	// Only cache instances with valid CLDR data (mData defined). If CLDR is not yet
-	// loaded, skip caching so the next call retries — preventing permanent poisoning
-	// of the cache with a broken instance.
 	if (!cache.has(locale)) {
 		// @ts-expect-error - The LocaleData constructor expects a LocaleT, but we are passing a Locale. This is a known issue and can be ignored for now.
 		// eslint-disable-next-line @typescript-eslint/no-unsafe-argument
-		const instance = new LocaleData(locale as unknown as LocaleT);
-		if (instance.mData) {
-			cache.set(locale, instance);
-		}
-		return instance;
+		cache.set(locale, new LocaleData(locale as unknown as LocaleT));
 	}
 
 	return cache.get(locale)!;

packages/main/src/Calendar.ts

@@ -644,12 +644,8 @@ class Calendar extends CalendarPart {
 		this._previousButtonDisabled = !this._currentPickerDOM._hasPreviousPage();
 		this._nextButtonDisabled = !this._currentPickerDOM._hasNextPage();
 
-		const localeData = getCachedLocaleDataInstance(getLocale());
-		if (!localeData.mData) {
-			return; // CLDR not yet loaded; reRenderAllUI5Elements will re-trigger once it is
-		}
-
 		const yearFormat = DateFormat.getDateInstance({ format: "y", calendarType: this.primaryCalendarType });
+		const localeData = getCachedLocaleDataInstance(getLocale());
 		this._headerMonthButtonText = localeData.getMonthsStandAlone("wide", this.primaryCalendarType)[this._calendarDate.getMonth()];
 		this._headerYearButtonText = String(yearFormat.format(this._localDate, true));
 

packages/main/src/DayPicker.ts

@@ -217,9 +217,6 @@ class DayPicker extends CalendarPart implements ICalendarPicker {
 
 	onBeforeRendering() {
 		const localeData = getCachedLocaleDataInstance(getLocale());
-		if (!localeData.mData) {
-			return; // CLDR not yet loaded; reRenderAllUI5Elements will re-trigger once it is
-		}
 		this._buildWeeks(localeData);
 		this._buildDayNames(localeData);
 	}