Machine Translation using seq2seq model
Clearly, the optimization of your loss function led to it only predicting the most common words in English. The probability of other words are obviously small. 
I am no expert, but I would check three things. 1. How long does it take for the loss to converge? With the output you show it is likely it does not take a long time. 2. Maybe try to filter out so you have different words in the sentences. 3. Check if it can help to optimize another loss function which would have a bias towards more diverse sentences.
I hope this can give you a few ideas at least.