Hi Aiman,
firstly, could you provide a link to a paper where you’re trying to implement the GEC model from (if that’s the case) as I’m not familiar with GEC.
However, aren’t your two field objects in the NMT code block redundant? Therefore the second implementation would be equal to the first one (assuming that ‘train.csv’ and ‘valid.csv’ have not changed).
As already mentioned, I’m not familiar with GEC models, but why don’t you just use an embedding layer?
Regards, 
Unity05