Maybe Cade and his gang only use bits and pieces of Huttese because they're not Hutts and don't know the language. They only use what they hear/catch on to. Also, words like "pateesta" and "e chu ta" are only short phrases, probably making it easier for a non-Huttese speaking person to use. Just like someone who doesn't speak Spanish would still undoubtedly know what "hola" meant through common outside usage.
And "War" is indeed the ending to "Legacy". "Legacy officially ended at issue #50, and "War" is a completely new title.