Add i18n Support to Backend

Describe what you are trying to accomplish and why in non technical terms
Currently, certain system messages lack multilingual support, including:

• Configuration file modification responses
• Error messages from functional modules
• Labels in GenAI requests

This creates usability barriers for non-English speaking users.

Describe the solution you'd like

For frontend-bound messages:

• APIs should return:

{
  "//": "↓↓ value: '{{camera}} load failed! Please check config.' ↓↓",
  "i18n_key": "camera_load_failed",
  "params": {"camera": "Camera Name"},
  "//": "Original message",
  "message": "Camera Name load failed! Please check config."
}

Regarding GenAI label localization:
The labels currently sent to AI service providers are monolingual, which may impact result accuracy. We propose having the backend directly fetch localized labels from i18n's objects.json language files to achieve proper multilingual support.

Describe alternatives you've considered
None

Additional context
None

Start by mapping the backend responses for configuration-file modifications and functional-module errors, then inspect the GenAI request path and the i18n objects.json language files. Define how localized labels and structured message fields should be returned across these areas; done means the affected messages and GenAI labels support the intended multilingual behavior.