What is the best way to write faster on Vim using a non-english keyboard?

I sympathize. You have at least a couple of options:

1. Since you said you'd love to buy an English keyboard, I'd recommend just changing your keyboard layout. on Windows you can do so under Regional Settings. On a basic Linux console you can use loadkeys. Under X11 you can use setxkbmap.
2. Just live with it the way it is. The vim help will make the most sense this way.
3. Search for a language map for your latin american keyboard. For instance, take a look at this one for dvorak.

I use the Dvorak keyboard layout and I just live with it the way it is. If there's a command or two that are very cumbersome, map them to something easy on your keyboard. There will inevitably be other shortcuts that are easier because of the different keyboard layout, but overall efficiency will depend on your layout and what features you use.