[MM3-users] change preferred language of list

hey, I am not very experienced with the mailman shell and configuration. I configured mailman using the mailman.cnf and I know that I can use "mailman conf" to get all the parameters. But now I would like to change the preferred language of a list. Because despite I set

[mailman] default_language: de

even new lists will still have "en" as preferred language. I checked this just by reading the $language variable in a list template. How can I change the list parameters and how can I make mailman to use the german language files? I found the files, so I know they exist, but still need to make mailman use them...