Until then
The German phrase 'Bis dahin' is used in a similar way to 'Until then' in English. It is often used to express a period of time until a certain event or situation occurs. For example, 'I will wait for you until then' could be translated to 'Ich werde auf dich warten bis dahin'.
Until then I had no idea that she would come
In this sentence, 'Bis dahin' is being used to express a time frame before a certain point in time. The speaker is stating that they had no idea about an event (she would come) until that particular point of time.
Everything was fine until then
Here, 'Bis dahin' is used to indicate that everything was fine up to a particular point in time. The inference is that things changed after this point.
The project must be completed by then
This sentence uses 'Bis dahin' to set a deadline. It indicates that the project should be completed before or by a certain point of time.