This problem started already more than a week ago.
When starting mkvtoolnix-gui I get following error:
terminate called after throwing an instance of ‘std::runtime_error’
what(): locale::facet::_S_create_c_locale name not valid
Tried reinstalling but did not help. Any idea how to solve this?
mkvtoolnix-gui-74.0.0-299.2.x86_64.rpm is the latest update (today updated) but problem remains.
Problem found but root cause unclear. With command: export LANG=C the problem is solved.
To me it looks that you have now documented it fairly clear and I think a bug report would be the next step.
(and do not forget to show your locale in the report.)