Multi-Language/ Seperate Dictionaries Support Needed

I have 3 languages installed (english, chinese and vietnamese), but the predction can't handle two or more languages. Languages in similar 'script' (vietnamese, eng, french, etc) are continually mixed-up within each sentence, regardless of which language is chosen (chinese is different). After trying an inferior samsung keyboard i realised they must use a seperate dictionary database for every language, as the languages are never jumbled - or at least some way of ensuring only one language's words can be drawn upon when that language is selected. Please please help improve this feature, as it's by far the best as a single-language keyboard, but really lacking for polyglots.

 Thank you very much