If a checksum word is present, language detection would use
just the word prefixes. However, a set of word prefixes may
be found in more than one language, and so the wrong language
may be found first, which could then fail the checksum, since
the check may be done with a different unique prefix length
from the one it was created from.
We now make a checksum test when we we detect a language from
prefixes only, to make sure we have the correct one.
f5f4109f9a