There are translations of the FET User manual in several languages http://lalescu.ro/liviu/fet/doc
I think it would be nice, when there is an User manual in the currently set language of the FET interface, by clicking on the Help -> Online -> Help contents the User manual in the language of the FET interface is opened.
Thank you for the suggestion! But I will only add it in the TODO, as I do not agree with it for now. I will think about it.