Tatsuo Ishii <ishii@postgresql.org> writes:
> similarity -> generate_trgm -> find_word -> iswordchr -> t_isalpha -> isalpha
> if locale is C and USE_WIDE_UPPER_LOWER defined which is the case in
> most modern OSs.
Quite. And *if locale is C then only standard ASCII letters are letters*.
You may not like that but it's not wrong; in fact any other behavior
would be wrong.
regards, tom lane