feat: add vietnamese ui language support

[naoNao89]

adds vietnamese locale support for the app and desktop ui

closes #29309

• add vi locale files for app, shared ui, and desktop
• register vi / vi-VN in app language settings
• register vi in desktop i18n
• keep README/docs untouched since README.vi.md already exists

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The following comment was made by an LLM, it may be inaccurate:

Potential Duplicate Found:

• PR feat(i18n): add Vietnam (vi) locale support #30102: feat(i18n): add Vietnam (vi) locale support
  • feat(i18n): add Vietnam (vi) locale support #30102

Why it's related: This PR also adds Vietnamese locale support with vi language code. Both PRs target the same feature (Vietnamese UI language support). You should verify whether PR #30102 is already merged or if it's still open, as it may duplicate the work in the current PR #31758.

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