I just imported the following translation file into PM 3.3.8:
https://ufpr.dl.sourceforge.net/project ... aker.fr.po
and I don't see any problems. Can you provide a screenshot of the problem?
I suspect that you opened the PO file and then saved the file in a character encoding that isn't UTF-8, which is what is causing the problem. (Linux usually uses UTF-8 by default, so it isn't a problem if you edit the PO file in Linux, but if you edit in a Windows System, you need to explicitly tell the text editor which character set you are using.)
I recommend that you download the French PO file again and import it into ProcessMaker and see if that fixes the problem.