Read the error message, it tells you everything you need to know:
FileNotFoundError: [Errno 2] No such file or directory: 'en_US.twitter.txt'
The file does not exists in the current folder. Possibly it exists in a different folder, or possibly it has a different name and / or extension - we can't tell.
Find the file, and add a path to it. We can't help you with that!