Sorry to bump this, but it’d be great to have some guidance here before setting up a new site (where the default language will be German).
Gerhard’s comments in the GitHub pull request sound like Discourse might already handle language settings internally/on a per column basis, but it’s hard for me to verify if this has been implemented, so I’m not sure whether the default locale of en_US.UTF-8 in app.yml is fine for a German site or not.