I have been seeing this happening more and more on our Moodle 3.5 environments but I cant seem to find the cause. Language packs seem to get messed up where they list other language packs as English and some strings show in English for the non primary packs are used by end users. Language customization for non primary packs will never show up.
The current fix for this is to just delete and re-add the language pack that is acting up but this has caused disruption for some of our end users and I have to constantly check things in the GUI as nothing seems to be out of the ordinary in moodledata.
Any help would be appreciated.