SwiftKey allows you to type seamlessly in up to five different languages without having to switch your settings.
Please ensure you have downloaded all your language packs (up to a maximum of five) and enabled them. For information on how to download a language, see here.
For languages with the same alphabet/layout, there is no need to switch between languages - you just start typing and SwiftKey figures out which language you are using!
For languages with different alphabets (i.e. English and Russian), simply slide left or right on the spacebar to switch between them.
Video captions are available here.