If I hardcode
Öé in my UTF-8 (according to PhpStorm and Sublime Text) PHP file, it's not converted to
Oe, but some gibberish.
Str::seemsUtf8 doesn't think it's UTF-8. If I force it to use the UTF-8 conversion, it works perfectly.
The not-used UTF-8 way works: https://3v4l.org/2EqNK
The used non-UTF-8 way doesn't work: https://3v4l.org/IoUYP
iconv() being decent with simple diacritics, but maybe not: https://3v4l.org/8QDlo