For SDL Trados Studio 2017 and Trados Studio 2015, the connection to Neural Machine Translation (NMT) is done through the Machine Translation Cloud Provider option, by installing the MT Cloud plugin, and no longer through the Language Cloud option.
Please find below an article that should help you with the steps to take to make the switch to the MT Cloud plugin:
https://gateway.sdl.com/apex/communityknowledge?articleName=000012630