Several mods affect this, as can be seen in their descriptions. You can probably do away with all of it by disabling Community Title Packs and Community Name Packs. Those are localised to be a Latin transcription of how they would have referred to themselves. For example, many Anglo-Saxons would have called themselves Ængles.

Aye removing CNP for UniUI and Community Title Pack seems to fix the problem.
thank you

In fact, this is anything but a bug. It is intentional. Some mods change the names to culture-specific names of the time and for provinces, for example (is the case for all titles) depends on which culture holds the province. Sometimes letters are used that are not found in all languages. The Æ in Ængle, for example, occurs in the Anglo-Saxon and Nordic languages. In German, it would be an Ä.

Since especially historically documented names from old languages are used, some names can become downright unpronounceable in some languages (I myself speak German as my native language. But the old German names are very, very difficult to read or even pronounce even for me). For lovers of historical immersion, however, this is very nice.

Edit: Since your original question was about how to turn this off: Some mods still come with some features. But I think a big part brings More Culture Names. As far as I know, the mod can be disabled without any problems.