I disagree with the translation of Je mange une crepe (circumflex over 1st e) au cafe: I translated it I am eating a crepe at a cafe; Duolingo says I am wrong, should be I am eating a crepe at the cafe. In idiomatic English, "the cafe" is awkward.
It depends on context. If you want to say you ate at the cafe and not at the restaurant, the translation with "the cafe" is right.
At a café would be dans un café. If you were on the phone talking to someone and they said "Where are you?", you could reply "I'm at the café" (assuming that you both frequented this café regularly....like on Friends or something.
Just my opinion.
If you want to be Duo-strict, you should translate as closely as possible to the original version you are given, even though it might sound weird in isolation (before and/or after translation).
Therefore, "correct" answers should be:
- with French first: je mange une crêpe au café => I eat a crêpe at the café
- with English first: I eat a crêpe at a café => je mange une crêpe dans un café.