According to the third edition of the Shorter Oxford Dictionary, an interjection is a grammatical term "expressing emotion, viewed as a Part of Speech." Wikipedia describes an interjection as "a word or expression that occurs as an utterance on its own and expresses a spontaneous feeling or reaction" that furthermore "partly overlaps with categories like profanities, discourse markers and fillers."
In German too, some interjections are also standard nouns, but most are basically sounds that express emotion. Here are some examples of German interjections that are nearly identical to English:
Jetzt weiß ich, warum wir verschlafen haben. -Aha, warum denn?
Now I know why we overslept. -Aha, why then?
Caption 53, Die Pfefferkörner: Cybermobbing
The next one is pretty easy, because even though it's spelled differently, it sounds the same:
Sonst gibt es keine Krone. -Autsch!
Otherwise there won't be any crown. -Ouch!
Caption 8, JoNaLu: Prinz Dreckspatz
The more common expression of pain in German, however, is aua, which is similar in sound to the English "ow."
Bingo, wir sind im Geschäft!
Bingo, we're in business!
Caption 61, Rücksicht im Verkehr: Christophorus
Es ist schön, dass wir in Deutschland sind. -Bravo.
It is nice that we are in Germany. -Bravo.
Caption 29, Deutschkurs in Tübingen: Die Konjunktion "dass"
There are also many German interjections that sound entirely different from their English counterparts:
Ach, ich bin klein!
Oh, I am small!
Caption 15, Deutschkurs in Tübingen: Obwohl
Na ja, wer's glaubt, wird selig.
Well, he who has faith shall be blessed.
Caption 12, Großstadtrevier: Von Monstern und Mördern
Mensch, wo bleibt sie denn?
Man, where is she then?
Caption 25, Die Pfefferkörner: Eigentor