This seems like a bug to me, but I'm just checking if we've overlooked something obvious. A user clicked the 'Deutsch' link on the login screen and Confluence happily changes to German - login screen, menus etc. That's fine. But there's no (obvious) way to switch back to English.
(We have a workaround - if you clear browser cookies, the German language setting goes away and English comes, but that's like thowing a hand grenade at the problem to fix it; there can be a lot of collateral damage and users don't like it.)
Shouldn't there be an "English" link on the login page to make it easy to switch back? This is Confluence v5.7.1