Enable translations

See https://docs.openedx.org/en/latest/developers/how-tos/enable-translations-new-repo.html

End result - there should be an openedx-core entry in https://github.com/openedx/openedx-translations/tree/main/translations

Also, go through the Makefile. Make sure all the translations-related targets work correctly, or are deleted if they're irrelevant.