Ok just to make sure we are doing the same thing since the iphone/ipad have several language options.
Here are my steps on the iPhone (same for iPad):
Go to Settings, then scroll down to "Language & Region", then the first option on that list says "iPhone Language" and it is marked English (on yours should say iPad language.
Press it, then select Espanol (spanish). It will tell you in spanish "cambiando idioma". which means changing language.
Then after a bit, the language of your phone should display spanish words.
At that point I just go into the app store, search for dogfight elite and install it. Run it. It runs the whole thing, video and all.
When I'm done with it, I just repeat the process to switch back to English. You don't need to change to Spanish to play Dogfight Elite, it is only the first time since it fails trying to find the english version of the video which is never played again after the first time.