You could do it like Chris said. But you could also create two different themings. One with a english.html and one with a german.html. Redirect the .com domain to english.html and redirect the .de to german.html. You can override the login page translations in the js files in the two different themings.
That way you have 1 application, but with two different languages. When the user is authenticated, your multilanguage forms will take over.
But you could also fix it by customizing the mendix login js by detecting the url in the browser and then translate the login page.
AFAIK you need two mendix application servers on the same database with different default languagues. Because the language is linked to the logged-in-user. You only know the language after login. As an alternative you can investigate on different login and index pages per language.