Istvan,
thanks for looking into this and adding information.
I do not feel competent to judge what the solution would be,
as I do not know the design goals of getlocale().
Given the documentation the function call would only make sense
if setlocale(getlocale(LC_XYZ)) would work in all cases, especially
after the locale has been set to the user preferances with setlocale(LC_ALL,"")
There is no simple test case that can make sure this is the case.

The workaround for current code for me is to use setlocale(LC_XYZ) only
to ask for the currently set locale and then decipher the string if the categories have different settings. This workaround can be seen in my
proposed test_case.py. 

I believe next steps could be to get a full overview and check design and
implementation, add some testcases so that more is covered and then fix 
the implementation. We could try to find out who invented getlocale
and ask.