Language menu/widget linking the same URL for all languages

Using pretty much bare-bones WP 3.9.1 and the recent Stella 1.4 (free) from May 2014.

I have used the language menu with two methods: automatically added to the navigation, and manually placed <?php the_widget( "Stella_Language_Widget"); ?> in my theme. In both cases, the ULRs generated by Stella in this menu are the same for all (in this case 2) languages: the standard URL without any language specifier in it.

I want to not use_hosts, i.e. the language should be encoded in the permalink. I have one example page, which provides the English content when accessed via …/en/…, and the German content when accessed without that specifier in the URL, i.e. the content is there and the Stella logic for interpreting this specifier works. However, the URL generation logic seems to be broken in my case.

Any pointers?

https://wordpress.org/plugins/stella-free/