Stereotypical GBA and DS bootlegs often try to look US English. Even if from countries that'd be unlikely to encounter in such amounts. I haven't looked into whether seeking UK or Australian versions is an effective way to avoid bootlegs. Might be interesting...
There's numerous details pirates may fail at: total incorrect art misshaped or no ESRB logo (for North American looking ones) battery in games that use flash saving only black cart of a color cart game
Though there are non-English fakes too! Look at this silly thing. http://www.ebay.com/itm/Pokemon-LeafGreen-Version-Japan-Game-Boy-Advance-GBA-/290842819813?pt=Video_Games_Games&hash=item43b7953ce5
What's the buzz? A high voltage positive ion attack!? Chaaa!
I have bought the bootleg version of Pokemon Sapphire which turn out to be a sequel to Pokemon Jade and Diamond. It's called Telefang 2: Speed (or Power? My friend had Pokemon Rubin which is the different version of it.) It was 9 years ago.
The game was generally a Pokemon's clone. You have your partner monster tag along with you. You can recruit new monsters, leveling up and have branch evolution. Battles are turn-based with very nice animation. (Some late game dragon have a skill that launch the enemies to the space with the rocket.)
It was all translated in English. Much to my surprise, I enjoy the game a lot until the battery of the cart died out. I can no longer find the translated version again.