And neither have I found any broken text with the new beta. Well done.
More details regarding the spoken Czech bug: I had App Language set to Default system, and that gave me all the dialogues in English, fine. I started navigating and Locus gave me directions in spoken Czech. When I minimised Locus, the text directions in the notifications were also in Czech. (OK, maybe it wasn't Czech but it looked like it, with your special characters.) When I checked the TTS setting, the TTS language was Czech (Czechia). That comes top of the list, which may be why it is preferred. My setting in Locus Pro is simply English and the app picks up my choice in Android settings of English (United Kingdom). In the beta it doesn't do that. I've been forced to choose English (United States), the only available English variant.
Neither, by the way, does Locus beta seem to pick up the Android system settings for speech rate (and possibly other settings). Locus now speaks directions very rapidly in an American accent.
There is one factor which may possibly be relevant: I'm away from home and working on mobile data not WiFi and Android is set to only download TTS data on WiFi.