Forgot to mention, you need to make sure that the language folder has the language files that you need.
Not the en_US.po or en_US.mo, that’s for English. For example, you need the zh_CN.po and zh_CN.mo for chinese language.
And also you need to switch your site language to the language that you want.
It’s located in WordPress admin -> Settings -> General at the end of the page.
Hope this helps.