Add simplified Chinese localization

[frto027]

• Fix a bug that Last updated not works.
• Add a component called LocalizedOutdateHint.vue, which shows a out-of-date hint when the translated file's last update time is behind the original file.
• Added some Simplified Chinese localization.

[overlappingd]

This is still on draft, but I would like to say something about the Simplified Chinese localization:
All translation efforts are managed using LingoHub, and aren't usually pull requested (as said in the README). If you'd like to further help with adding Simplified Chinese localization, you can apply here (Make sure you're in the BSMG discord).

[qe201020335]

Hi @overlappingd
I asked about Simplified Chinese localization in bsmg today. Blookcloak told me to simply create a PR because "the organizational effort has fizzled out due to lack of time".
If you have access to LingoHub, do you mind checking whether there is any localization work for Simplified Chinese already done? In case there are any, I think we can incorporate the changes there so we are not doing duplicate work.
Blookcloak just told me that we have migrated from LingoHub to Crowdin and I got the access to Crowdin.