Skip the English idioms and focus on what really matters
English idioms are fun to learn (and teach!), but do you really need to learn them? The answer is usually "no", especially if you are working with other non-native speakers who most likely wouldn't know them either.
It's true that native speakers often use English idioms. In fact, many probably don't realize they are using them, which is the main problem. Even if you don't understand an idiom completely, you can probably use the context of the situation and other cues -- such as the content before and after the idiom, and the body language of the speaker -- to guess whether it was a positive, negative, funny and/or serious statement.
In a worst case, you can ask for clarification, but that probably won't be necessary.
- Learning English idioms is an endless task. Your time is probably better spent focusing on other aspects of learning English.
- Just as English idioms don't have a 1 to 1 translation into German, most German idioms can't be translated 1 to 1 into English. Rather than try to translate "alles ist im grünen Bereich", it's better to use a clear and simple equivalent, such as "everything is okay".
And finally, which English idioms would have been possible to use in this blog post?
until you're blue in the face
until the cows come home
to bite off more than you can chew
to avoid something like the plague
to spin your wheels
time is money