Hi, @biotopsocken.
Make sure the option: “You will need to configure DNS subdomains on your site.”, it’s checked. If so, you will have to create subdomains.
I recommend you change this option to (
Panel > Settings> Languages): URL Modification Mode = “Use Pre-Path Mode (Default, puts /en/ in front of URL). SEO friendly.” and checked “Hide URL language information for default language.”.