It’s a staging site. Can that be the issue?
If I fill in translates on the site, when will they be published? In the next updates? I see in German there are quite some strings missing… https://translate.wordpress.org/projects/wp-plugins/download-manager/dev/de/formal?filters%5Bstatus%5D=untranslated&sort%5Bby%5D=priority&sort%5Bhow%5D=desc&page=3
