XF 1.5 Not showing correct language

[Triops]

I have set "Deutsch" as default languages in both, menu languages and Options -> Appearance:




But all (most?) of my visitors (all Germans with German browser and OS settings) get English when first visiting the forums after launch.
What do I have to set mor, please?

 

[Triops]

I see... probably English was set from import? Of course, will write now German ID to all users in database.