"Der Präsident muss mit dem Kongress reden."
Übersetzung:The President needs to talk to Congress.
Here "Congress" is being used as a proper noun, thus the capital letter. Presumably this was said in the president's country about the congress of that country. There's no reason this couldn't be said as "The president needs to talk to the congress", although that's more context specific ex. "The president is visiting (random country) this week, and while there he intends to talk to the congress of (that country).
It's interesting that "President" is considered a proper noun by the author. I guess it could be a proper noun for the same reason I just gave for "Congress", but it seems really bizarre ro me. Maybe it's just because I'm from a country that doesn't have a president.