Update translations.js to add Chinese (Simplified) and Chinese (Traditional)

[lakejason0]

I'm using this greeter theme starting today because I hate to have a functional GNOME while actually using KDE (sddm has some bug so I had to give up). It's a really nice lightdm theme, but it can be better to have Chinese support!
I don't know whether it supports language fallback (because there are many "variants" of Chinese, and all of them eventually can be split into Simplified and Traditional). That is, "zh_Hant" "zh_TW" "zh_HK" (idk if there's more in Linux locale) should use "zh_TW" texts in the translation. "zh_CN" (and if there's "zh_Hans" or more Linux locale) should use "zh_CN" texts in the translation. "zh" is for fallback of Chinese, and idk if I should actually set this to any of them, but by default in MediaWiki "zh" is fallback to "zh_CN".
Hope that you can accept my pull request.

[lakejason0]

Also, Chinese doesn't (I even should use "never") use italic text, because it would cause a legibility issue. Though I have a relatively big screen and the text size is relatively big in the theme, it might still be a problem. I'll appreciate it if you can look into the problem but this is totally another problem.

[Litarvan]

I edited the theme so that when chinese is detected, the usage of italic is disabled text :)
Thanks a lot for your contribution!