Fix various Expressive Code translation issues (#1708)

Co-authored-by: Chris Swithinbank <357379+delucis@users.noreply.github.com>
Co-authored-by: Hippo <6137925+hippotastic@users.noreply.github.com>

5 files changed, 163 insertions, 19 deletions

diff --git a/.changeset/wet-lemons-drum.md b/.changeset/wet-lemons-drum.md
new file mode 100644
index 00000000..79a013a9
--- /dev/null
+++ b/.changeset/wet-lemons-drum.md
@@ -0,0 +1,5 @@
+---
+'@astrojs/starlight': patch
+---
+
+Fixes translation issues with Expressive Code when using a default language other than English
diff --git a/packages/starlight/__tests__/i18n/translations-ec.test.ts b/packages/starlight/__tests__/i18n/translations-ec.test.ts
new file mode 100644
index 00000000..cbefb76f
--- /dev/null
+++ b/packages/starlight/__tests__/i18n/translations-ec.test.ts
@@ -0,0 +1,117 @@
+import { pluginFramesTexts } from 'astro-expressive-code';
+import { afterEach, expect, test, vi } from 'vitest';
+import { addTranslations } from '../../integrations/expressive-code/translations';
+import { StarlightConfigSchema, type StarlightUserConfig } from '../../utils/user-config';
+
+vi.mock('astro-expressive-code', async () => {
+	const mod = await vi.importActual<typeof import('astro-expressive-code')>(
+		'astro-expressive-code'
+	);
+	return {
+		...mod,
+		pluginFramesTexts: {
+			...mod.pluginFramesTexts,
+			overrideTexts: vi.fn(),
+		},
+	};
+});
+
+afterEach(() => {
+	vi.clearAllMocks();
+});
+
+test('adds default english translations with no i18n config', async () => {
+	const [config, useTranslations] = getStarlightConfigAndUseTranslations(undefined);
+
+	addTranslations(config, useTranslations);
+
+	expect(getExpressiveCodeOverridenLanguages()).toEqual(['en']);
+});
+
+test('adds translations in a monolingual site with english as root locale', async () => {
+	const [config, useTranslations] = getStarlightConfigAndUseTranslations({
+		root: { label: 'English', lang: 'en' },
+	});
+
+	addTranslations(config, useTranslations);
+
+	expect(getExpressiveCodeOverridenLanguages()).toEqual(['en']);
+});
+
+test('adds translations in a monolingual site with french as root locale', async () => {
+	const [config, useTranslations] = getStarlightConfigAndUseTranslations({
+		root: { label: 'Français', lang: 'fr' },
+	});
+
+	addTranslations(config, useTranslations);
+
+	expect(getExpressiveCodeOverridenLanguages()).toEqual(['fr']);
+});
+
+test('add translations in a multilingual site with english as root locale', async () => {
+	const [config, useTranslations] = getStarlightConfigAndUseTranslations({
+		root: { label: 'English', lang: 'en' },
+		fr: { label: 'French' },
+	});
+
+	addTranslations(config, useTranslations);
+
+	expect(getExpressiveCodeOverridenLanguages()).toEqual(['en', 'fr']);
+});
+
+test('add translations in a multilingual site with french as root locale', async () => {
+	const [config, useTranslations] = getStarlightConfigAndUseTranslations({
+		root: { label: 'French', lang: 'fr' },
+		ru: { label: 'Русский', lang: 'ru' },
+	});
+
+	addTranslations(config, useTranslations);
+
+	expect(getExpressiveCodeOverridenLanguages()).toEqual(['fr', 'ru']);
+});
+
+test('add translations in a multilingual site with english as default locale', async () => {
+	const [config, useTranslations] = getStarlightConfigAndUseTranslations(
+		{
+			en: { label: 'English', lang: 'en' },
+			fr: { label: 'French' },
+		},
+		'en'
+	);
+
+	addTranslations(config, useTranslations);
+
+	expect(getExpressiveCodeOverridenLanguages()).toEqual(['en', 'fr']);
+});
+
+test('add translations in a multilingual site with french as default locale', async () => {
+	const [config, useTranslations] = getStarlightConfigAndUseTranslations(
+		{
+			fr: { label: 'French', lang: 'fr' },
+			ru: { label: 'Русский', lang: 'ru' },
+		},
+		'fr'
+	);
+
+	addTranslations(config, useTranslations);
+
+	expect(getExpressiveCodeOverridenLanguages()).toEqual(['fr', 'ru']);
+});
+
+function getStarlightConfigAndUseTranslations(
+	locales: StarlightUserConfig['locales'],
+	defaultLocale?: StarlightUserConfig['defaultLocale']
+) {
+	return [
+		StarlightConfigSchema.parse({
+			title: 'Expressive Code Translations Test',
+			locales,
+			defaultLocale,
+		}),
+		vi.fn().mockReturnValue(() => 'test UI string'),
+	] as const;
+}
+
+function getExpressiveCodeOverridenLanguages() {
+	return [...new Set(vi.mocked(pluginFramesTexts.overrideTexts).mock.calls.map(([lang]) => lang))];
+}
diff --git a/packages/starlight/integrations/expressive-code/index.ts b/packages/starlight/integrations/expressive-code/index.ts
index 0c1a0af6..fc9962f8 100644
--- a/packages/starlight/integrations/expressive-code/index.ts
+++ b/packages/starlight/integrations/expressive-code/index.ts
@@ -77,7 +77,6 @@ export function getStarlightEcConfigPreprocessor({
 	return (input): AstroExpressiveCodeOptions => {
 		const astroConfig = input.astroConfig;
 		const ecConfig = input.ecConfig as StarlightExpressiveCodeOptions;
-		const { locales } = starlightConfig;
 
 		const {
 			themes: themesInput,
@@ -111,7 +110,7 @@ export function getStarlightEcConfigPreprocessor({
 		});
 
 		// Add Expressive Code UI translations (if any) for all defined locales
-		if (useTranslations) addTranslations(locales, useTranslations);
+		if (useTranslations) addTranslations(starlightConfig, useTranslations);
 
 		return {
 			themes,
@@ -124,6 +123,7 @@ export function getStarlightEcConfigPreprocessor({
 				}
 				return theme;
 			},
+			defaultLocale: starlightConfig.defaultLocale?.lang ?? starlightConfig.defaultLocale?.locale,
 			themeCssSelector: (theme, { styleVariants }) => {
 				// If one dark and one light theme are available, and the user has not disabled it,
 				// generate theme CSS selectors compatible with Starlight's dark mode switch
diff --git a/packages/starlight/integrations/expressive-code/translations.ts b/packages/starlight/integrations/expressive-code/translations.ts
index 1ff1c286..7aa5a4a1 100644
--- a/packages/starlight/integrations/expressive-code/translations.ts
+++ b/packages/starlight/integrations/expressive-code/translations.ts
@@ -1,26 +1,37 @@
 import { pluginFramesTexts } from 'astro-expressive-code';
 import type { StarlightConfig } from '../../types';
 import type { createTranslationSystemFromFs } from '../../utils/translations-fs';
+import { localeToLang } from '../shared/localeToLang';
 
 export function addTranslations(
-	locales: StarlightConfig['locales'],
+	config: StarlightConfig,
 	useTranslations: ReturnType<typeof createTranslationSystemFromFs>
 ) {
-	for (const locale in locales) {
-		const lang = locales[locale]?.lang;
-		if (!lang) continue;
-
-		const t = useTranslations(locale);
-		const translationKeys = [
-			'expressiveCode.copyButtonCopied',
-			'expressiveCode.copyButtonTooltip',
-			'expressiveCode.terminalWindowFallbackTitle',
-		] as const;
-		translationKeys.forEach((key) => {
-			const translation = t(key);
-			if (!translation) return;
-			const ecId = key.replace(/^expressiveCode\./, '');
-			pluginFramesTexts.overrideTexts(lang, { [ecId]: translation });
-		});
+	addTranslationsForLocale(config.defaultLocale.locale, config, useTranslations);
+	if (config.isMultilingual) {
+		for (const locale in config.locales) {
+			if (locale === config.defaultLocale.locale || locale === 'root') continue;
+			addTranslationsForLocale(locale, config, useTranslations);
+		}
 	}
 }
+
+function addTranslationsForLocale(
+	locale: string | undefined,
+	config: StarlightConfig,
+	useTranslations: ReturnType<typeof createTranslationSystemFromFs>
+) {
+	const lang = localeToLang(config, locale);
+	const t = useTranslations(locale);
+	const translationKeys = [
+		'expressiveCode.copyButtonCopied',
+		'expressiveCode.copyButtonTooltip',
+		'expressiveCode.terminalWindowFallbackTitle',
+	] as const;
+	translationKeys.forEach((key) => {
+		const translation = t(key);
+		if (!translation) return;
+		const ecId = key.replace(/^expressiveCode\./, '');
+		pluginFramesTexts.overrideTexts(lang, { [ecId]: translation });
+	});
+}
diff --git a/packages/starlight/integrations/shared/localeToLang.ts b/packages/starlight/integrations/shared/localeToLang.ts
new file mode 100644
index 00000000..5d79d017
--- /dev/null
+++ b/packages/starlight/integrations/shared/localeToLang.ts
@@ -0,0 +1,11 @@
+import type { StarlightConfig } from '../../types';
+
+/**
+ * Get the BCP-47 language tag for the given locale.
+ * @param locale Locale string or `undefined` for the root locale.
+ */
+export function localeToLang(config: StarlightConfig, locale: string | undefined): string {
+	const lang = locale ? config.locales?.[locale]?.lang : config.locales?.root?.lang;
+	const defaultLang = config.defaultLocale?.lang || config.defaultLocale?.locale;
+	return lang || defaultLang || 'en';
+}