fix: not work detectBrowserLanguage on client-side correctly (#2475)

* fix: not work detectBrowserLanguage on client-side correctly

* fix

Author: kazupon

specs/fixtures/issues/2473/app.vue

@@ -0,0 +1,3 @@
+<template>
+  <NuxtPage />
+</template>

specs/fixtures/issues/2473/locales/en-US.json

@@ -0,0 +1,15 @@
+{
+  "Meta": {
+    "locale": "English"
+  },
+  "Pages": {
+    "Home": {
+      "title": "Home page",
+      "description": "Home page description"
+    },
+    "About": {
+      "title": "About page",
+      "description": "About page description"
+    }
+  }
+}

specs/fixtures/issues/2473/locales/fr-FR.json

@@ -0,0 +1,15 @@
+{
+  "Meta": {
+    "locale": "French"
+  },
+  "Pages": {
+    "Home": {
+      "title": "Page d'accueil",
+      "description": "Page d'accueil description"
+    },
+    "About": {
+      "title": "À propos",
+      "description": "A propos description"
+    }
+  }
+}

specs/fixtures/issues/2473/nuxt.config.ts

@@ -0,0 +1,22 @@
+import type { LocaleObject } from '#i18n'
+
+const locales = [
+  { code: 'en', iso: 'en-US', file: 'en-US.json' },
+  { code: 'fr', iso: 'fr-FR', file: 'fr-FR.json' }
+] as LocaleObject[]
+
+const defaultLocale = locales[0]
+
+export default defineNuxtConfig({
+  modules: ['@nuxtjs/i18n'],
+  i18n: {
+    locales,
+    defaultLocale: defaultLocale.code,
+    langDir: 'locales/',
+    lazy: true,
+    strategy: 'no_prefix',
+    detectBrowserLanguage: {
+      fallbackLocale: defaultLocale.code
+    }
+  }
+})

specs/fixtures/issues/2473/package.json

@@ -0,0 +1,14 @@
+{
+  "name": "nuxt3-test-issues-2473",
+  "private": true,
+  "scripts": {
+    "build": "nuxt build",
+    "dev": "nuxt dev",
+    "generate": "nuxt generate",
+    "preview": "nuxt preview"
+  },
+  "devDependencies": {
+    "@nuxtjs/i18n": "latest",
+    "nuxt": "latest"
+  }
+}

specs/fixtures/issues/2473/pages/about.vue

@@ -0,0 +1,6 @@
+<template>
+  <h1 id="title" v-text="$t('Pages.About.title')" />
+  <p v-text="$t('Pages.About.description')" />
+  <p v-text="$t('Meta.locale')" />
+  <NuxtLinkLocale id="locale" to="/">{{ $t('Pages.Home.title') }}</NuxtLinkLocale>
+</template>

specs/fixtures/issues/2473/pages/index.vue

@@ -0,0 +1,6 @@
+<template>
+  <h1 id="title" v-text="$t('Pages.Home.title')" />
+  <p v-text="$t('Pages.Home.description')" />
+  <p v-text="$t('Meta.locale')" />
+  <NuxtLinkLocale id="locale" to="/about">{{ $t('Pages.About.title') }}</NuxtLinkLocale>
+</template>

specs/issues/2473.spec.ts

@@ -0,0 +1,28 @@
+import { test, expect, describe } from 'vitest'
+import { fileURLToPath } from 'node:url'
+import { URL } from 'node:url'
+import { setup, url, createPage } from '../utils'
+import { getText } from '../helper'
+
+describe('#2473', async () => {
+  await setup({
+    rootDir: fileURLToPath(new URL(`../fixtures/issues/2473`, import.meta.url))
+  })
+
+  test('should be respected detect browser language', async () => {
+    const home = url('/')
+    const page = await createPage(undefined, { locale: 'fr' })
+    await page.goto(home)
+
+    expect(await getText(page, '#title')).toEqual(`Page d'accueil`)
+
+    // change page
+    await page.locator('#locale').click()
+    await page.waitForURL('**/about')
+    expect(await getText(page, '#title')).toEqual(`À propos`)
+
+    // one more change page
+    await page.locator('#locale').click()
+    expect(await getText(page, '#title')).toEqual(`Page d'accueil`)
+  })
+})

src/runtime/internal.ts

@@ -335,7 +335,7 @@ export function detectBrowserLanguage<Context extends NuxtApp = NuxtApp>(
 
   // browser locale detection happens during first access only
   if (!firstAccess) {
-    return { locale: '', stat: false, reason: 'first_access_only' }
+    return { locale: strategy === 'no_prefix' ? locale : '', stat: false, reason: 'first_access_only' }
   }
 
   const { redirectOn, alwaysRedirect, useCookie, fallbackLocale } =