fix(NcDateTimePicker): use translated words in dates formatted with a format string

build/date-fns-locales-plugin.mts

@@ -0,0 +1,62 @@
+/*!
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: CC0-1.0
+ */
+import type { Plugin } from 'vite'
+
+import { exactRegex } from '@rolldown/pluginutils'
+import { glob } from 'fs/promises'
+import { createRequire } from 'module'
+import { dirname, join } from 'path'
+
+/**
+ * This plugin generates a module that can be used to dynamically load locales from `date-fns`.
+ * It generates it in a way that it works with the externalization of the `date-fns` locales
+ * and with Vite and Webpack apps.
+ *
+ * A plugin is used because Vite's dynamic imports and glob imports cannot generate imports in such a way.
+ */
+export default () => {
+	let localeFiles: string[] = []
+	const virtualModuleId = 'virtual:date-fns-locales'
+	const resolvedVirtualModuleId = '\0' + virtualModuleId
+	return {
+		name: 'date-fns-locales-plugin',
+		enforce: 'pre',
+		async buildStart() {
+			this.info('Collectioning locales in date-fns/locales')
+			const require = createRequire(import.meta.url)
+			const pkgJsonPath = require.resolve('date-fns/package.json')
+			const localeDir = join(dirname(pkgJsonPath), 'locale')
+			localeFiles = await Array.fromAsync(glob('*.js', {
+				cwd: localeDir,
+				exclude: ['types.js', 'en-US.js', 'cdn.js', 'cdn.min.js'],
+			}))
+		},
+		resolveId: {
+			filter: { id: /dateFnsLocaleLoader\.ts$/ },
+			handler() {
+				return resolvedVirtualModuleId
+			},
+		},
+		load: {
+			filter: { id: exactRegex(resolvedVirtualModuleId) },
+			handler() {
+				let content = ''
+				content += 'const loader = {}\n'
+				content += 'export default loader\n'
+				for (const localeFile of localeFiles) {
+					// e.g., "pt-BR.js" -> "pt-BR"
+					const localeCode = localeFile.slice(0, -3)
+					let exportName = localeCode.replaceAll('-', '')
+					// One locale is named inconsistently...
+					if (localeCode === 'be-tarask') {
+						exportName = 'beTarasak'
+					}
+					content += `loader['${localeCode}'] = async () => (await import('date-fns/locale/${localeCode}')).${exportName}\n`
+				}
+				return content
+			},
+		},
+	} as Plugin
+}

package.json

@@ -137,6 +137,7 @@
     "@playwright/test": "^1.61.1",
     "@types/gettext-parser": "^9.0.0",
     "@types/node": "^26.0.1",
+    "@types/webpack-env": "^1.18.8",
     "@vitest/coverage-v8": "^4.1.9",
     "@vue/test-utils": "^2.4.6",
     "@vue/tsconfig": "^0.9.1",

playwright.config.ts

@@ -64,6 +64,8 @@ export default defineConfig({
 
 		ctViteConfig: async () => ({
 			plugins: [
+				// Add to support multiple locales
+				(await import('./build/date-fns-locales-plugin.mts')).default(),
 				// normally added by default but we overwrite the plugins so we need to add it back manually
 				(await import('@vitejs/plugin-vue')).default(),
 				// We do have some dependencies that use node modules -> we need to polyfill

src/components/NcDateTimePicker/NcDateTimePicker.vue

@@ -293,6 +293,7 @@ import NcIconSvgWrapper from '../NcIconSvgWrapper/NcIconSvgWrapper.vue'
 import NcTimezonePicker from '../NcTimezonePicker/NcTimezonePicker.vue'
 import { t } from '../../l10n.ts'
 import NcButton from '../NcButton/index.ts'
+import useDateFnsLocale from './useDateFnsLocale.ts'
 
 type LibraryFormatOptions = VueDatePickerProps['format']
 
@@ -539,6 +540,8 @@ const placeholderFallback = computed(() => {
 	return t('Select date and time')
 })
 
+const dateFnsLocale = useDateFnsLocale(realLocale)
+
 /**
  * The date (time) formatting to be used by the library.
  * We use the provided format if possible, otherwise we provide a formatting function
@@ -775,7 +778,12 @@ function sameDay(a: Date, b: Date): boolean {
 
 <template>
 	<div class="vue-date-time-picker__wrapper">
+		<!-- Setting :key="dateFnsLocale.code" forces the component to rerender when `:formatLocale` changes.
+             Without it, the formatted date only changes after the user focuses on the text input.
+             This issue was only observed with :format="realFormat" being a pattern, e.g., 'dd MMM yyyy'.
+             See https://github.com/Vuepic/vue-datepicker/issues/1284  -->
 		<VueDatePicker
+			:key="dateFnsLocale.code"
 			ref="picker"
 			:aria-labels
 			:autoApply="!confirm"
@@ -787,6 +795,7 @@ function sameDay(a: Date, b: Date): boolean {
 			:placeholder="placeholder ?? placeholderFallback"
 			:format="realFormat"
 			:locale="realLocale"
+			:formatLocale="dateFnsLocale"
 			:minDate="calcMinMaxTime.minDate"
 			:maxDate="calcMinMaxTime.maxDate"
 			:minTime="calcMinMaxTime.minTime"

src/components/NcDateTimePicker/dateFnsLocaleLoader.ts

@@ -0,0 +1,38 @@
+/*!
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+/// <reference types="@types/webpack-env" />
+
+import type { Locale } from 'date-fns'
+
+// This is only required for `npm run styleguide`.
+// For `npm run build`, `npm run dev` and everything else using Vite
+// all the code from this file is overriden by `build/date-fns-locales-plugin.mts`.
+const webpackContext = import.meta.webpackContext('../../../node_modules/date-fns/locale', {
+	recursive: false,
+	regExp: /\.js$/,
+	exclude: /(types|en-US|cdn(\.min)?)\.js$/,
+	mode: 'lazy',
+})
+
+/**
+ * Given a `key` load the locale from the webpack context.
+ *
+ * @param key File name for the locale e.g., ./nl-BE.js'
+ */
+async function loadLocale(key: string) {
+	const mod = await webpackContext<Promise<{ default: Locale }>>(key)
+	return mod.default
+}
+
+const loader: Record<string, () => Promise<Locale>> = {}
+
+for (const key of webpackContext.keys()) {
+	// Remove prefix `./` and suffix `.js` to get the locale code.
+	const localeCode = key.slice(2, -3)
+	loader[localeCode] = () => loadLocale(key)
+}
+
+export default loader

src/components/NcDateTimePicker/useDateFnsLocale.ts

@@ -0,0 +1,42 @@
+/*!
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+import type { Locale } from 'date-fns'
+import type { ComputedRef, MaybeRefOrGetter } from 'vue'
+
+import { computedAsync } from '@vueuse/core'
+import { enUS } from 'date-fns/locale/en-US'
+import { computed, toValue } from 'vue'
+import loader from './dateFnsLocaleLoader.ts'
+
+/**
+ * Given a locale try to load the corresponding locale from date-fns.
+ * Fall back to en-US while loading, if the request locale does not exist or could not be loaded.
+ *
+ * @param locale locale code (e.g., 'de-DE')
+ */
+export default function useDateFnsLocale(locale: MaybeRefOrGetter<string>): ComputedRef<Locale> {
+	const loadedLocale = computedAsync(() => loadDateFnsLocale(toValue(locale)))
+	return computed(() => loadedLocale.value ?? enUS)
+}
+
+/**
+ * Given a locale code load the locale from the loader.
+ *
+ * @param locale Locale code (e.g, nl-BE.js)
+ */
+async function loadDateFnsLocale(locale: string): Promise<Locale | undefined> {
+	if (locale in loader) {
+		return await loader[locale]()
+	}
+
+	if (locale.includes('-')) {
+		// Try without region
+		const shortLocale = locale.split('-')[0]
+		return loadDateFnsLocale(shortLocale)
+	}
+
+	return undefined
+}

tests/component/components/NcDateTimePicker.spec.ts

@@ -62,6 +62,27 @@ for (const [type, modelValue, locale, expectedValue] of l10nTestcases) {
 	})
 }
 
+const customFormatTestcases = [
+	['date', 'yyyy MMM dd', new Date(2000, 9, 2), 'de-DE', '2000 Okt. 02'],
+	['date-range', 'dd MMM yyyy', [new Date(2000, 0, 1), new Date(2000, 9, 7)] as [Date, Date], 'es-ES', '01 ene 2000 - 07 oct 2000'],
+	['date', 'EEEE d MMMM yy', new Date(2026, 9, 2), 'ru', 'пятница 2 октября 26'],
+	['month', 'LLLL yy', new Date(2026, 9, 2), 'ru', 'октябрь 26'],
+] as const
+for (const [type, format, modelValue, locale, expectedValue] of customFormatTestcases) {
+	test(`Handle format ${format} for type ${type} with locale ${locale}`, async ({ mount, page }) => {
+		page.addScriptTag({ content: `document.getElementsByTagName('html')[0].dataset.locale = "${locale}";` })
+		await mount(NcDateTimePicker, {
+			props: {
+				modelValue,
+				format,
+				type,
+			},
+		})
+
+		await expect(page.getByRole('textbox')).toHaveValue(expectedValue)
+	})
+}
+
 test('Today is selected by default', async ({ mount, page }) => {
 	await page.clock.setSystemTime(new Date(2000, 0, 22))
 

vite.config.ts

@@ -9,6 +9,7 @@ import { createLibConfig } from '@nextcloud/vite-config'
 import { globSync } from 'glob'
 import { join, resolve } from 'node:path'
 import { defineConfig } from 'vite'
+import dateFnsLocalesPlugin from './build/date-fns-locales-plugin.mts'
 import vueDocsPlugin from './build/docs-plugin.ts'
 import l10nPlugin from './build/l10n-plugin.mjs'
 import packageJson from './package.json' with { type: 'json' }
@@ -31,6 +32,7 @@ const entryPoints = {
 const overrides = defineConfig({
 	plugins: [
 		vueDocsPlugin,
+		dateFnsLocalesPlugin(),
 		l10nPlugin(resolve(import.meta.dirname, 'l10n')),
 	],
 	css: {
@@ -71,7 +73,7 @@ export default defineConfig((env) => {
 		// By default all dependencies are external, but no path imports
 		nodeExternalsOptions: {
 			// Packages with paths imports should be added here to mark them as external as well
-			include: [/^@nextcloud\/.+\//, /^@mdi\/svg\//],
+			include: [/^@nextcloud\/.+\//, /^@mdi\/svg\//, /^date-fns\/locale\//],
 			// Make sure to not provide uncompiled vue files as dependencies, this will break unit tests
 			exclude: [/\.vue(\?|$)/],
 		},