We're told that localizing the Skype app for MacOS is complex but achievable via iLocalize. Again, Skype is hazy on details. If you have experience doing this and especially if you know a way of recycling the Windows .lang strings, let us know?
Based on our limited information, we have so far ascertained the following:
File are located in
/Applications/Skype.app/Contents/Resources
It is possible to copy (for example) de.lproj to cy.lproj - which works if your locale is cy_GB.
However, there are some 85 files in that directory which would have to be handled individually on Transifex which would be a pain to work with. A possible option would be to merge them and then de-merge them.
May be relevant that Transifex supports the Mac file format:
http://docs.transifex.com/formats/apple-strings/
Different projects use different formats, the Apple stuff appears to be in bplist00, Microsoft Office is in a binary format.
Transifex only supports the .strings version, so this may still be something to consider for other projects. Mac does have a 'lbtool' utility to convert between formats, but it was of no use in producing a xliff file for Skype.