[php-src] Issue #8096: mb_convert_case($str, MB_CASE_TITLE, "UTF-8"); doesn't convert the Greek last letter to ς but to σ

Issue: https://github.com/php/php-src/issues/8096 Comment Author: nikic Yes, we certainly do not depend on locales for this purpose. In fact, we have made good progress on eliminating locale-dependent functionality, with the most recent step being https://wiki.php.net/rfc/strtolower-ascii. I think basing this off mbstring.language is viable, though we'd want to make sure that the language can also be passed explicitly to the relevant case-conversion functions, so as to avoid dependence on global state. I don't think that adding per-language functions makes sense. Supporting Turkish case folding rules at least would probably be of some value, as the way dotted i is handled under default case folding is often perceived as undesirable (creates I with an additional combining mark). I believe we already special-case one Turkish legacy encoding in this regard.