No Language Auto detect in OneNote 2013
Unfortunately there seems to be no working auto-detection of frequently-used languages in OneNote 2013. However this works fine in Word 2013. This video is a side-by-side comparison of both applications using English and German as languages to be detected.
Also see this Office support links for further information:
http://off365.ms/5uQVCg
http://off365.ms/XhO7AC
And this tweet: / 479755739754663937