fix(translations): adjust some zh translations (#13867)

This PR corrected and adjusted some zh translations. Also added space
between number/letter and Chinese chars.

BTW, I noticed that:

1) When bulk select medias, the `select` button's label is untranslated,
but I couldn't find it here.
2) The README under `/translations` says `zh-Hans` and `zh-Hant`, but
the language codes are `zh` and `zh-TW`. Shall we update the README as
well? But personally, `zh-Hans` & `zh-Hant` would be better.

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Co-authored-by: Dan Ribbens <dan.ribbens@gmail.com>

Author: escwxyz