If LastIndexOf returns -1 (no "." found) this may cause issues. It's a bit of an edge case, but in theory, a package called "en" with a language "en" would be assumed to be a satellite package, despite not following the rules in our spec.

I'm OK with the argument that: "That's an edge case, whatever" but maybe add a "&& suffixIndex > 0" clause to the if to prevent that?