Switching languages does not work for me well. I type in 3 languages, two of them has accents. I usually type in different language than is set in the keyboard, because I forgot to set it. My phone keyboard (default on galaxy s3) has learned it well, so it is not problem. I have another recomendation:

Let user to check which languages he is using (somewhere in settings) and then allow him to use them as he wish. Mix all selected languages into one, previous (or two previous word) should be enough to predict correct next word.