and how do you get there when the default language is something I do not understand and cannot read. It says set default language during the setup but that fails as the default language appears to be cz
If you take the top one from the list of languages, you select the system standard. If your phone is set to French, Mapfactor will switch to French.
I have used many versions, both default play store as well as experimental versions, using clean installs. In all occurrences mapfactor always selected either English or the system standard language (my phone's standard) as the default language.