Environment

• Operating System: Linux
• Node Version: v23.11.1
• Nuxt Version: 3.17.4
• CLI Version: 3.25.1
• Nitro Version: 2.11.12
• Package Manager: npm@11.4.0
• Builder: -
• User Config: compatibilityDate, devtools, modules, i18n, devServer
• Runtime Modules: @nuxtjs/i18n@9.5.5
• Build Modules: -

Reproduction

Minimal repo here https://github.com/ThibaudDauce/test_i18n

This is my app.vue:

<template>
  <div>
    <p>{{ $t('Hello {name}', { name: 'John' }) }}</p>
    <p>{{ $t('The weather today is {condition}!', { condition: 'sunny' }) }}</p>
  </div>
</template>

With this i18n/i18n.config.ts:

export default defineI18nConfig(() => {
  return {
    missingWarn: false,
    formatFallbackMessages: true,
  }
})

And this nuxt.config.ts:

export default defineNuxtConfig({
  compatibilityDate: '2025-05-15',
  devtools: { enabled: true },
  modules: ['@nuxtjs/i18n'],
  i18n: {
    defaultLocale: 'fr',
  },
  devServer: {
    port: 8080,
  },
})

missingWarn: false is working so the config seems to be loaded correctly.

Describe the bug

When I set formatFallbackMessages: true, the messages are not formatted in the template.