journal: avoid buffer overread when locale name is too long

journal: avoid buffer overread when locale name is too long

We could potentially create an unterminated string and then call normal string
operations on it. Let's be more careful: first remove the suffix we ignore anyway,
then find if the string is of acceptable length, and possibly ignore it if it
is too long. The code rejects lengths above 31 bytes. Language names that are
actually used are much shorter, so this doesn't matter much.