Does EASA approve the use of localizer back course?
Depends what you mean. If you mean "are they approved at EASA airports?" I can't help except to say that I have never seen a plate for one, flying into most EASA countries into a wide variety of airports.

If you mean "are EASA aircraft and pilots allowed to fly them in countries that do allow them?", I can tell you that in the Radio Navigation syllabus for the EASA ATPL exams there is a learning objective that the student must know what to set on an OBS or HSI to fly a back-beam localiser approach (if you want to check it's LO 062.02.05.02.08 in the new syllabus, 062.02.05.02.13 in the old one which is just about to go out but more widely available at the moment). This implies that flying one in an EASA-registered aircraft with an EASA licence and IR is not prohibited.