feat(i18n): fallback to en when i18n is incomplete

[SkyeYoung]

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Why submit this pull request?

• Bugfix
• New feature provided
• Improve performance
• Backport patches

What changes will this PR take into?

As described in #3140, https://www.i18next.com/principles/fallback#language-fallback provides the functionality of fallback to the default language, which can be configured directly to achieve the function.

OLD	NEW

Now, untranslated text will use the en text, while translated text will use the corresponding language's i18n.

example:

// zh/common.json
{
  "sources": {
    "consumers": "消费者"
  }
}

I found that the menu style after the language is selected was not provided before during development, and I will create a separate PR to implement it later.

Related issues

fix/resolve #3140

Checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?
• Is this PR backward compatible? If it is not backward compatible, please discuss on the mailing list first