Is this with Python 3.8 on Windows? If so there was a change in Python where it sets the locale during startup instead of just ignoring it and doing nothing as it did in prior versions. Since that caused wx’s locale to be out of sync there would be mismatch errors raised from wx.
I added some code to try and bring the two back in sync, but maybe something more needs to be done, or something done differently. You can see the code in wx/core.py in the
App.InitLocale method if you (or anybody) feel like experimenting and finding a solution.