About [[MediaWiki:Categorytree-member-num/en]]
This message says "Don't translate this message." in its documentation, but what if I want to localize parentheses?
To avoid any need to translate this message maybe it can be written as {{int:parentheses|$5}}.
Not sure exactly why this warning exists. I think it's meant to say that you should only translate it if needed (i.e optional), but don't use more parameters, or parser functions for the out of the box translation. Having different parentheses is an excellent reason to make a translation in Chinese.