I followed the link you provided and they share an “el.mo” file. I guess I shouldn’t have spent 7 hours last night translating mu..
Anyway, my problem wasn’t the file, I already had mine. The directory I’ve put it in is “/wp-content/plugins/buddypress/bp-languages/” and it’s named buddypress-el_GR.mo. I saw in another thread that the directory should be “/wp-content/mu-plugins/buddypress/bp-languages/”, is that my fault?
I also changed the language in the wp-config.php file to “define (‘WPLANG’, ‘el’);” and it didn’t work, so I created a folder named “languages” in “/wp-content/”. It still didn’t work.
No, wpmu is in english.. I renamed the files to buddypress-el_GR.po and buddypress-el_GR.mo but still no change. The country code and language code are correct, because I found them in wordpress documentation.