Pokemon codes: How do they work

[PokemonORAS]

So my cousin who lives in another country that doesn't distribute codes wants a NA code from me (I am in NA BTW). Can I send one to him and will it still work? My cousin has an Asian DS (I believe) and an Asian game (I believe. I may be wrong since they got 2 copies and sent one to me and my NA codes work on that game but they have the DS language set to Asian which is why I think it's an Asian game.)

I was wondering how the code system works. Specifically can I use NA codes on other country 3DS? Can I use NA codes on different country games? Most importantly, can I use NA code on an NA game on another country 3DS (or vice versa. NA code, diff game, NA 3DS).

Thanks for your help guys!