Providing that the set_locale( LC_ALL, "" ) call is the only place I don't think it would be too hard to replace "" with a command line value if its present. But I don't know if thats all that is needed?
Not sure it'd be really easy to do, since IIRC we set locale before parsing arguments to let e.g. --help be translated.
Hmm, potential problem all right.
And again, I'm not sure there's much use case for this... if one wants all hes app use the C locale, just set the system locale.
Yes, perhaps its easier to have a script that sets LANG and runs Geany, call that from the desktop menu and alias geany to it for the command line.
Cheers Lex