there should not be any reason for not allowing: You know each other? It is quite common in English to simply use the voice inflection to ask the question and this is indicated by the question mark. The Romanian sentence relies on this and you already allow this form as an alternative in other languages.
You should “report” that instead of posting it here. The course is still in beta, and missing alternative translations are to be expected.
To me 'You know each other?'is not the same as 'Do you know yourselves'. The former is knowledge of others in a group, whereas the latter is referring to individual introspection within a group of people.