It's a simple concept, crude, but effective (there are probably better ways to do it but this method is easy to implement).

Say you have 2 source files, A and B.

A is a capture of the audio and video from your VHS tape; audio is in synch.
B is the video from the French retail DVD.

You edit A so that it is exactly the same as B - same total length, scene changes are at the same frame numbers and so on, then you save out the audio. This audio will be an exact sync match for the video from B.