I just tested on my Pro1x with LOS. I think it works there. That is (just to confirm I know what is being talked about). I added Dansk (Denmark) to my list of system languages (the main one is US English). When I go to type in an editor, I am typing in English. and then I hold the yellow arrow and press spacebar and I get a notification that I am now typing in Dansk and I can get that weird ae mashup ;-). I can use the yellow arrow spacebar as a toggle between the two.
Doesn't work on my Pro1. yellow arrow + spacebar pulls up search. Don't know why. My Pro1 is currently Google Free