Hello there, Vicvic. In response to your question, it would be relatively
simple to make the English audio of the subtitled version match with the French version, surely much easier than those who "De-Specialize" Star Wars. Though your two Othellos are virtually the same version, they are probably different transfers, meaning slightly different timing so the audio won't sync perfectly with no editing.
You just need to "rip" the video of the French version onto your computer in a format which can be opened by editing software and in a quality high enough to determine what the characters are saying; you then "rip" the audio of the subtitled version. In some cheap video editing software, you can trim the audio where necessary in order to get it to sync, matching their mouths. You just then need to export the audio in an .ac3 format and then pair it up with a lossless version (an m2v video file) of your French version. Then you should have a DVD ready to burn. I have a feeling I'm making this whole thing sound more complicated than it is; there may be guides online that explain better.
There is one difference between the two versions: after Desdemona's death, there is a close-up of her dead in the French dubbed version. There is no corresponding shot in the subtitled version, presumably censored. You should handle this as you see fit. I don't believe there are other differences, but someone please correct me if I'm wrong.
Alternatively, I believe there is a copy of the Othello European cut in English without subtitles floating around trade circles. If you're trying to get the American version of Othello (IMO, a superior edit), then you may as well try to get this one too and save yourself the trouble of syncing audio. Anyway, good luck, VicVic. It's a shame there's no official release, making this whole thing much easier.