my Plex account settings are set to english. My OS is set to english. My browser is set to english. Yet Plex/Web decided to switch to German. For no apparent reason, the whole UI is in German now. Luckily, I speak German. However, this still sucks. Massively.
Whatever you did there, PlexDevs, please revert that and obey my account language setting.
The language setting of Plex Web is solely defined by what is set under
Settings - Plex Web - General
or
Einstellungen - Plex Web - Allgemein
If you have activated the syncing of settings in the web app, all web browsers which are logged into your plex account are unified in regard to settings. Now if you have somewhere opened a web browser for someone else to look at in german, this setting may have propagated to your other web browsers.
You can this button in Settings - Plex Web - General - ‘Show Advanced’