Somehow, the parameter `format_module_path` was never used, only in that one failint test in `i18n/tests.py` - that test should have used `with self.settings(FORMAT_MODULE_PATH='foobar')` instead of passing in this parameter.

However, that parameter must be there for some reason and other people might use it in their codebases, so I changed the code slightly to honour the parameter again. If the parameter is given, we ignore the setting.