Language translation breaks site (.mo / .po)

I was able to understand this issue. For some reason my page.php wasn’t handling the translation properly (probably the internal wordpress redirection to single-course.php), while everything works fine without the translation, when it’s on the loop break and index.php is always displayed.

Changed my custom page.php to generatepress theme page.php and the loop was working fine. Managed to make changes to do_action and now everything is working again, even with translation on.