freak wrote:

This backend uses mb_check_encoding to make sure everything used in queries is always in the right encoding. It might be removed at some point, but for now it requires php to have mbstring enabled (i.e.: --enable-mbstring)

Hope this helps in any way ...

languages/Language.php sets mb_internal_encoding('UTF-8'), so the check in DatabaseOracle.php checks for valid UTF-8.

AFAIK, throughout the rest of MediaWiki, mbstring is always optional.

To check for valid UTF-8, DatabaseOracle.php could use the same technique as Language::checkTitleEncoding(), which uses preg_match if mb_check_encoding is not available.

Proposed fix in Gerrit: https://gerrit.wikimedia.org/r/31141