From 359a64219288795936f18fd50fb5f195c412a748 Mon Sep 17 00:00:00 2001
From: HiDeoo <494699+HiDeoo@users.noreply.github.com>
Date: Wed, 10 Jul 2024 18:06:13 +0200
Subject: [PATCH] =?UTF-8?q?Fix=20an=20Astro=20i18n=20=E2=86=92=20Starlight?=
 =?UTF-8?q?=20i18n=20config=20conversion=20issue=20(#2122)?=
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---
 .changeset/large-bananas-beg.md                  |  5 +++++
 packages/starlight/__tests__/basics/i18n.test.ts |  4 ++--
 packages/starlight/utils/i18n.ts                 | 11 ++++++-----
 3 files changed, 13 insertions(+), 7 deletions(-)
 create mode 100644 .changeset/large-bananas-beg.md

diff --git a/.changeset/large-bananas-beg.md b/.changeset/large-bananas-beg.md
new file mode 100644
index 00000000000..0e22d385a67
--- /dev/null
+++ b/.changeset/large-bananas-beg.md
@@ -0,0 +1,5 @@
+---
+'@astrojs/starlight': patch
+---
+
+Fixes an i18n configuration issue for multilingual sites when using Astro’s `i18n` config with `prefixDefaultLocale` set to `false`.
diff --git a/packages/starlight/__tests__/basics/i18n.test.ts b/packages/starlight/__tests__/basics/i18n.test.ts
index 527783b9a01..32dd299aae1 100644
--- a/packages/starlight/__tests__/basics/i18n.test.ts
+++ b/packages/starlight/__tests__/basics/i18n.test.ts
@@ -162,7 +162,7 @@ describe('processI18nConfig', () => {
 					locales: ['en', { codes: ['fr'], path: 'french' }],
 				},
 				expected: {
-					defaultLocale: { label: 'English', lang: 'en', dir: 'ltr', locale: 'en' },
+					defaultLocale: { label: 'English', lang: 'en', dir: 'ltr', locale: undefined },
 					locales: {
 						root: { label: 'English', lang: 'en', dir: 'ltr' },
 						french: { label: 'Français', lang: 'fr', dir: 'ltr' },
@@ -180,7 +180,7 @@ describe('processI18nConfig', () => {
 					routing: { prefixDefaultLocale: false },
 				},
 				expected: {
-					defaultLocale: { label: 'فارسی', lang: 'fa', dir: 'rtl', locale: 'fa' },
+					defaultLocale: { label: 'فارسی', lang: 'fa', dir: 'rtl', locale: undefined },
 					locales: {
 						root: { label: 'فارسی', lang: 'fa', dir: 'rtl' },
 						de: { label: 'Deutsch', lang: 'de', dir: 'ltr' },
diff --git a/packages/starlight/utils/i18n.ts b/packages/starlight/utils/i18n.ts
index 8cba4f5a2bb..ce07b1cc4d8 100644
--- a/packages/starlight/utils/i18n.ts
+++ b/packages/starlight/utils/i18n.ts
@@ -118,11 +118,12 @@ function getStarlightI18nConfig(
 		locales,
 		defaultLocale: {
 			...inferStarlightLocaleFromAstroLocale(defaultAstroLocale),
-			locale: isMonolingualWithRootLocale
-				? undefined
-				: isAstroLocaleExtendedConfig(defaultAstroLocale)
-					? defaultAstroLocale.codes[0]
-					: defaultAstroLocale,
+			locale:
+				isMonolingualWithRootLocale || (isMultilingual && !prefixDefaultLocale)
+					? undefined
+					: isAstroLocaleExtendedConfig(defaultAstroLocale)
+						? defaultAstroLocale.codes[0]
+						: defaultAstroLocale,
 		},
 	};
 }