[KevinH]

Originally Posted by BeckyEbook

This is intentionally limited to commonly used Latin-based European characters (PL, CZ, SK, SI, HR, LT, LV, EE, DE, AT, CH, FR, ES, PT, IT, NO, SE, DK, FI, NL, HU, RO).
Non-Latin scripts (CJK, RTL, etc.) are deliberately excluded and will continue to fall back to Python on demand.

static const QString XHTML_CHARS =
    "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
    "1234567890!@#$%^&*()_-+={}[]:;\"'<>,.?/|\\…„”“’»«"
    "ąćęłńóśżźĄĆĘŁŃÓŚŻŹáàâäãåÁÀÂÄÃÅéèêëÉÈÊËíìîïÍÌÎÏ"
    "òôöõøÓÒÔÖÕØúùûüÚÙÛÜýÿÝŸçÇñÑšžŠŽđĐœæŒÆß";

P.S. I also added some punctuation marks.

Wonderful. I will modify CodepointNames.cpp to pre-cache those as well.

Update: I have pushed this change to master.