This thread is resolved. Here is a description of the problem and solution.
FAT Event - The calendar's months and days translation does not show on the front-end
Those strings are currently "untranslatable". They are hardcoded in JS files. When deactivating WPML and setting the site language to German, the issue still happens. Even with the .po files for German in place. We suggest checking with the plugin author, as those strings are probably not properly localized.
This is the technical support forum for WPML - the multilingual WordPress plugin.