vue-i18n-skilld

vue-i18n 11.4.12 (Vue 3)

Internationalization plugin for Vue.js.

• Peer dependency: vue ^3.0.0 (package.json:44). No Vue 2 support; use vue-i18n v8 for Vue 2.
• Node engines: >= 22 (package.json:47).
• For Nuxt 3, use @nuxtjs/i18n instead of installing this directly (https://vue-i18n.intlify.dev/guide/integrations/nuxt3.html).

Core rules

1. Default to Composition API mode. Pass legacy: false to createI18n and use useI18n(). Legacy API mode (legacy: true, the default) is deprecated in v11 and removed in v12 (dist/vue-i18n.d.ts:1728).
2. Do not use the v-t directive in new code. Deprecated in v11, removed in v12 (dist/vue-i18n.d.ts:2138). Use t(), $t, or the <i18n-t> component.
3. tc and $tc no longer exist. Dropped in v11; t/$t handle pluralization via the plural option (verified: no tc export in dist/vue-i18n.d.ts).
4. Interpolation uses {name} syntax. The v8 modulo % syntax was dropped in v10 (https://vue-i18n.intlify.dev/guide/migration/breaking10.html#drop-modulo-syntax).
5. Messages are compiled at runtime (JIT) by default since v10. For CSP-strict environments or best performance, pre-compile with @intlify/unplugin-vue-i18n (https://vue-i18n.intlify.dev/guide/advanced/optimization.html).
6. Never interpolate user input into messages rendered with v-html without escapeParameter: true; translate content, do not concatenate HTML.

Setup

// i18n.js
import { createI18n } from 'vue-i18n'

const i18n = createI18n({
  legacy: false, // Composition API mode
  locale: 'ja',
  fallbackLocale: 'en',
  messages: {
    en: { message: { hello: 'hello world' } },
    ja: { message: { hello: 'こんにちは、世界' } }
  }
})

export default i18n

// main.js
import { createApp } from 'vue'
import App from './App.vue'
import i18n from './i18n'

createApp(App).use(i18n).mount('#app')

app.use(i18n) installs the $t/$d/$n/$rt global properties (when globalInjection: true, the default), enables useI18n, and globally registers i18n-t, i18n-d, i18n-n (when globalInstall: true, the default; dist/vue-i18n.d.ts:1810-1822).

Translate in a component

<script setup>
import { useI18n } from 'vue-i18n'
const { t, locale } = useI18n()
</script>

<template>
  <h1>{{ t('message.hello') }}</h1>
  <p>{{ t('greeting', { name: 'Kyoko' }) }}</p>
  <p>{{ $t('message.hello') }}</p><!-- works in templates via globalInjection -->
</template>

Call useI18n() inside setup only. It throws "Must be called at the top of a setup function" otherwise.

Common tasks

Pluralize. Message: 'no apples | one apple | {count} apples' (pipe-separated forms, selected by plural rules for the locale).

t('apple', count, { count }) // or t('apple', { count }, choice)

Custom rules: pluralRules on Composer options (Composition), pluralizationRules (Legacy).

Format dates and numbers.

const { d, n } = useI18n()
d(new Date(), 'long') // named format from datetimeFormats option, else Intl fallback
n(1234567, 'currency') // named format from numberFormats option

Interpolate components. Use <i18n-t keypath="..." tag="p"> with slot children per placeholder; see components.

Switch locale. locale.value = 'en' from a Composer; also update the document lang attribute and, on SSR, the Accept-Language handling (https://vue-i18n.intlify.dev/guide/advanced/lazy.html).

Lazy load locales. Dynamic import() plus setLocaleMessage / mergeLocaleMessage; see optimization.

Type-safe keys

Augment the global DefineLocaleMessage, DefineDateTimeFormat, DefineNumberFormat interfaces to get key completion and inference in useI18n without generics; see typescript.

Pitfalls

• useI18n({ messages: ... }) creates a local scope; without useScope: 'global' local messages do not merge with global ones (https://vue-i18n.intlify.dev/guide/essentials/scope.html).
• $t in templates requires globalInjection: true in Composition mode (dist/vue-i18n.d.ts:1735-1746).
• Vue warns about a missing locale message with key fallback to the key itself; configure missing/missingWarn/fallbackWarn to control noise.
• Linked messages (@:key), literal { }, and @ | in messages need escaping; see message-syntax.
• Do not import from deep paths such as vue-i18n/dist/* in bundler projects; use the package root so the correct build resolves (package.json:63-83).

Migration status

Change	Version	Action
Legacy API mode deprecated	v11	Move to legacy: false before v12 (dist/vue-i18n.d.ts:1728)
v-t directive deprecated	v11	Replace with t()/$t/<i18n-t> (dist/vue-i18n.d.ts:2138)
tc/$tc removed	v11	Use t/$t plural option
JIT message compilation default	v10	Pre-compile for strict CSP
% named interpolation removed	v10	Use {name}
$t positional overload changed	v10	Pass plural via options object

Details: migration.

References

• composition-api: createI18n, useI18n, Composer members, scopes, locale switching
• message-syntax: interpolation, pluralization, linked messages, HTML safety
• components: i18n-t, i18n-n, i18n-d
• formats: datetime and number formatting, custom format definitions
• typescript: schema typing, generated locale types
• optimization: tree shaking flags, pre-compilation, lazy loading, dist files
• migration: v9, v10, v11 breaking changes and v12 removals
• legacy-api: Legacy API mode surface still present in v11

Official documentation: https://vue-i18n.intlify.dev/ API reference: https://vue-i18n.intlify.dev/api/general.html Changelog (cited, not copied): https://github.com/intlify/vue-i18n/blob/master/CHANGELOG.md