Buy MacBook Air with Spanish keyboard?

It depends on where you are located. If Spanish is not the normal language of your country, you would probably have to order it from the Apple online store and have it shipped to you or to a nearby store for pickup.

Whether the online store in your country sells Spanish keyboard machines you can find out by just going to the website and pretending you are buying one. Apple stores do not sell outside their own country.

In any case, you need to contact Apple stores directly yourself, nobody in these forums represents Apple sales or any store.