I made a translation request on r/translation for one of my uploads, and I got what seemed to be a pretty solid one. Are these types of externally-sourced translations allowed?
Just based on the amount of comments I've seen under translated posts along the lines of "translation from reddit user ILikeFrogs420" etc I assume it is fine with permission/credit.
If you're unsure of the accuracy, you can use the check translation tag. Though as the tag's wiki mentions, it should not be used as an excuse for posting substandard translations as posting bad translations is more detrimental than posting no translation at all.