From what I know, it is possible to change the checkout language as well:
I don't know if Shoppers can choose language on exit - Best to get a test shop and test it out for yourself. Its what am going to do.
That article is from 2006. You can only specify ONE language for your checkout. Sure, you can make your checkout Chinese.. but if your main site is Dutch... checkout will still be Chinese.
That is not the same as checkout adjusting to your language.
Good point! If you are fine having both languages side by side simply create a checkout tranlsation for your shop that suits your needs.