add: zh-Hans translate

[qingyiwebt]

Add a zh-Hans (Simplified Chinese) translate for Beutl, most strings are translated, but some are still in progress.
This pr can be merged directly, and I will continue translating and fixing some problems in my spare time.

[yuto-trd]

Thank you!
The commit message includes “WIP”, but is it okay to merge this PR? Or would it be better to wait until the translation is complete? Please let me know which option would make it easier for you to proceed with the remaining work.

[qingyiwebt]

Both are OK, it seems that the need for CN translate is not in a hurry, so the pr can be merged after the translate is completed.
Commits will be added to this pr after I make progress in translating.

[yuto-trd]

Got it. Then, Could you set the PR status to draft until the work is done?

[qingyiwebt]

OK, I have set it to draft status.

[qingyiwebt]

I also found some places not actually read from translate file, like:

[yuto-trd]

Thank you for pointing that out. I’ve added it to the translation file in this commit, so please try rebasing with the main branch.
3b9feea

Additions:

• Strings
  • ExtensionsSettings
    • en: "Extensions Settings"
    • ja: "拡張機能の設定"
  • AboutBeutl
    • en: "About Beutl"
    • ja: "Beutlについて"