Don't suppose anybody wants to tackle a translation plugin for Friendica... (?)
Unfortunately I believe the only realistic provider choices are Google and Bing. Google is now solidly on the dark side (and is closing access to the translation API) and Microsoft defined evil software.
I suppose if there are any free machine translators they're likely to be poor as you need a huge corpus of translated material to get good at it (such as a search engine has). Still if there was something that sort of worked, I'd prefer a free and open translation service over the two evils.