Support for translation of messages from the server

[karelkryda]

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Description

Currently, messages returned from the server are displayed in English. If the user chooses a different language, it would be useful to display the messages from the server in their chosen language as well.

This PR returns messages from the server as keys for i18n (instead of the default English texts), which are then translated.

Type of change

Please delete any options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• User interface (UI)
• Translation update

Checklist

• My code follows the style guidelines of this project
• I ran ESLint and other linters for modified files
• I have performed a self-review of my own code and tested it
• I have commented my code, particularly in hard-to-understand areas
  (including JSDoc for methods)
• My changes generate no new warnings
• My code needed automated testing. I have added them (this is optional task)

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[louislam]

This PR returns messages from the server as keys for i18n (instead of the default English texts), which are then translated.

I thought this approach before too, but there are two things may have to be aware of.

1. Some error messages could be dynamic.
2. Uptime Kuma API could be possibly available in the future (Add foundation for API development #1834). As an API, if an error msg is a key that may not be helpful.

[CommanderStorm]

@karelkryda
Could you close this PR in favor of #3263?
I think the approach is similar enough and mentioned PR is closer to be mergable

[CommanderStorm]

Thanks ^^