Don't include locales which only have rails translations in
the candidates, and ensure that user specified options take
priority over less specific variants of earlier choices.
Minitest 6 will not allow assert_equal to compare for equality
with nil and minitest 5 has already started warning about it.
That's fine if you're comparing with a nil constant, but if you're
comparing with an expression that is sometimes nil and sometimes
not nil it's an absolute pain in the rear end.
