Change default language

I bought a macbook air from someone on ebay- went and picked it up. Anyway, I have come to reinstall Mountain Lion from my USB stick, and when I boot from it, the language is set as Polish (the seller was Polish!). When i boot from my USb on my new retina, it's in english so it's clearly something to do with the system settings.

I know when I first created a user account, I could change the language settings etc from within my user account to English, but I cannot figure out how to make it display in English when I reinstall the OS.

I'm now selling it after buying a 13" retina, but I want to leave it at the welcome screen for the new buyer. Only problem is, I don't want it in Polish!

Anyone have any ideas on how to solve this?! I've tried logging into the user account, going to terminal and choosing english using the sudo languagesetup command, but it's still polish when I boot from USB

Thanks in advance!

 

So an internet restore didn't work either. The 'please select your region' is the first screen i come to, and even if i select united kingdom its still Polish!

How come it doesnt take me to the 'please select your language' screen first?!