Questions related with languages, micropayment and building apks

Hi, I hope there isn't any problem for asking several questions at once.

I'm about to finish my first game for the android market. It's a logic puzzle with more than 100 levels.

At the beginning of the game it asks you what language you want to play in (Spanish, English or French), but I was wondering if there is a way in unity to detect the device language to avoid asking that question to the user.

Next: Since the android market is so populated with games, it will be hard to sell, so I was thinking of offering half the game for free and the rest you can buy if you like it with a micropayment. I read that unity offers the tools to do so, but I can't find where the tools are or what they are called. Can anybody please tell me where or how I should look for that information? Thanks!

And the last one: I tried to install my game (.apk) on my new android phone (a Monte Carlo from Orange, an european operator, with android version 2.3.5) While the game size is 6Mb, the installation only ocupies 112kbs on the phone and when I attempt to launch the game, it crashes with just an "unexpected error". Since I have no information on the error, I don't know where to start looking for solutions. Any help?

This thing is really frustrating, because I tried the game on many other devices (phones, tablets), with higher and lower versions of android, and it always worked.

Thanks for all your help.