Translation:You were very beautiful at the restaurant yesterday.
Agreed, as of 3/15/2020 the tts still clips at the end of güzel(din). Which is too bad since this word is crucial to understanding what is happening in this sentence. The ending -din is the clue that the sentence is directed towards "you" , as in "you were beautiful at the restaurant last night".
I thought the same in the beginning but when I looked at the sentence again, restoranDA has the suffix that shows location, so if they were talking about the restaurant being beautiful they would have just said restoran or restorani maybe. And also it says güzeldin which is directed to 'you' (2nd person) not to 'he/she(/it)'. If it was about the restaurant (3rd person) the verb would be in the form 'güzeldi'. So overall maybe something like "Dün restorani çok güzeldi"
It's been ten months since you posted the question, so I hope you're not stuck anymore and didn't give up learning. Keep going strong:)