Erm, I wouldn't try doing that.
In any case, did you download all the assets too? The installer should have obtained them for you. If you're unsure, look for an .Unvanquished directory in your home folder. You should see all the pak.pk3 files, and the latest vms.pk3. If not, you can find them on our SourceForge page.
If it's not an asset issue, then there's something with the installer. In that case, you have a few options. You can compile from source, if you know how to do that. If not, you can download the PlayDeb version, which should work just fine, assuming they've updated it for the current month. Or, since you're on a Debian derivative, you might be able to get our Debian packages working for you.