I guess it is a known problem since the Linux program explicitly uses "python2.5" to run pre-compiled code.
It would be nothing but a regular dependency if it wasn't for the fact that python 2.5 is phased out, so my Linux system doesn't have it in its normal packages anymore.
Just thought I'd report what happens on a up-to-date Linux system with these Python 2.5 precompiled binaries.
If I switch interpreter to Python 2.7, when running gmail-backup-gui.sh, I get the following error message:
RuntimeError: Bad magic number in .pyc file