fix: fix loading fallback locale with lazy loading

src/plugins/main.js

@@ -143,6 +143,12 @@ export default async (context) => {
     // Lazy-loading enabled
     if (lazy) {
       const { loadLanguageAsync } = require('./utils')
+
+      // Load fallback locale.
+      if (app.i18n.fallbackLocale && newLocale !== app.i18n.fallbackLocale) {
+        await loadLanguageAsync(context, app.i18n.fallbackLocale)
+      }
+
       await loadLanguageAsync(context, newLocale)
     }
 

test/fixture/basic/lang/en-US.js

@@ -0,0 +1,6 @@
+export default {
+  home: 'Homepage',
+  about: 'About us',
+  posts: 'Posts',
+  untranslated: 'in english'
+}

test/fixture/basic/pages/fallback.vue

@@ -0,0 +1,3 @@
+<template>
+  <h1>{{ $t('untranslated') }}</h1>
+</template>

test/module.test.js

@@ -131,6 +131,54 @@ describe('basic', () => {
   })
 })
 
+describe('lazy loading', () => {
+  let nuxt
+
+  beforeAll(async () => {
+    const override = {
+      i18n: {
+        lazy: true,
+        langDir: 'lang/',
+        vueI18n: {
+          fallbackLocale: 'en'
+        }
+      }
+    }
+
+    const testConfig = loadConfig(__dirname, 'basic', override, { merge: true })
+
+    // Override those after merging to overwrite original values.
+    testConfig.i18n.locales = [
+      {
+        code: 'en',
+        iso: 'en-US',
+        name: 'English',
+        file: 'en-US.js'
+      },
+      {
+        code: 'fr',
+        iso: 'fr-FR',
+        name: 'Français',
+        file: 'fr-FR.js'
+      }
+    ]
+    testConfig.i18n.vueI18n.messages = null
+
+    nuxt = (await setup(testConfig)).nuxt
+  })
+
+  afterAll(async () => {
+    await nuxt.close()
+  })
+
+  test('shows fallback string', async () => {
+    const html = await get('/fr/fallback')
+    const dom = getDom(html)
+    const title = dom.querySelector('h1')
+    expect(title.textContent).toBe('in english')
+  })
+})
+
 describe('no_prefix strategy', () => {
   let nuxt