Do I need to know all translations?
Many word and sentence cards list more than one translation on their back. So, do you need to know all the translations in order to treat a card as "learned"?
Ultimately, this is your decision, and a question of your personal learning style. However, we recommend to not try to learn all translations of a word or phrase - at least as long as you are not at level Advanced. For the beginning, it is much more important to learn at least one translation of a word or phrase, and to be able to use it in a sentence. This is the most important part of learning a language: being able to communicate.
So, if you look at the front of a card, and you immediately know one of the translations listed on the back, then you can safely grade this card with easy or too easy.
The more you advance with your language skills, the more nuances of the language you know - and want to know. For Advanced users, it might make sense to expect more than one translation - especially the most important translations, which are at the top of the back side.
In the end, this is up to you. The more you use the app, the more you are able to just decide when you want to see the card again.
I always forget about one of the translations, and I want to learn it
If you would like to learn a specific translation of a word, you can add its example sentence as a separate card. This will make sure that you learn to translate this word in this specific context.