fallback locale deep key using `tm` throw error

[Gavin Luo]

Reporting a bug?

When a deep not exist current locale, but exist in fallback locale, it will throw error Cannot read properties of null (reading 'xxx')

Expected behavior

Use the value from the fallback locale

Reproduction

https://stackblitz.com/edit/vitejs-vite-zkwein?file=src%2FApp.vue,src%2Fmain.ts

System Info

System:
    OS: Linux 5.0 undefined
    CPU: (4) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 0 Bytes / 0 Bytes
    Shell: 1.0 - /bin/jsh
  Binaries:
    Node: 18.18.0 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 10.2.3 - /usr/local/bin/npm
    pnpm: 8.14.0 - /usr/local/bin/pnpm
  npmPackages:
    @vitejs/plugin-vue: ^4.2.3 => 4.3.4 
    vite: ^4.4.9 => 4.4.9 
    vue: ^3.3.4 => 3.3.4 
    vue-i18n: ^9.3.0 => 9.3.0 
    vue-tsc: ^1.8.8 => 1.8.10

Screenshot

No response

Additional context

No response

Validations

• Read the Contributing Guidelines
• Read the Documentation
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Check that this is a concrete bug. For Q&A open a GitHub Discussions

[kazuya kawaguchi]

Unfortunately, vue-i18n expects the message retrieved by tm to be an array, and the use case expectation is to resolve it using rt.
It also expects the messages retrieved in the array to have the same structure in this case en and ja.

If your application assumes a different message structure, as in this case, you will need to do the validation yourself.