sometimes newt just makes up words while he's talking. his brain will either mash two similar or related words together, or just string together random sounds in the middle of his sentence, and sometimes he notices and stops to try and find the actual word, but a lot of the time he doesn't even realise and just keeps talking. Sometimes, particularly when he hasn't slept or seen the sun in a while, Hermann will start sprinkling German or Yiddish words into largely English sentences, just using whatever word best fits his purpose regardless of what language it's from. The reason they don't even question their drift compatibility when it comes down to it is because (even though Newt doesn't know a lot of German or Yiddish) they always understand eachother perfectly.