Actually SwiftKey in multiple languages helps me write in the ones I am less fluent in, due to its autocorrect. I agree it can be annoying too... you have to be careful with activating languages, and I switch off the languages I am unlikely to use in the near future.

Still miss my BB though.

Edited to add: unlike other commenters here, I never use the glide feature in Swiftkey! I just use it as a better keyboard...