I am currently on Drupal 7.38 but I have been having this issue as long as I remember. Search by any string that contains non-ASCII returns no result, e.g., "praça", "ヒロ”, etc.
Search Simple CJK option is enabled. Index is 100%. Tried re-indexing multiple times. Rerunning cron often. Again, all ASCII strings are working as expected.
You can imagine I have been googling for answers like a mad man for many years, finally decided to ask here. Any pointer would be appreciated.