You use a translation! :)
I have no qualms about using translations when learning sentences – the first time you see them.
My rule is that no translations are allowed on the flashcards. So the stuff you see every day can’t have English. You need to add enough image-based cues so that you don’t need to see your translation ever again.
PS: You don’t always NEED translations – if you know most of the words in a sentence then you can often figure out the meaning via context, but I don’t have any problem with translations to learn sentences the first time you see them.