Street Fighter III/WMG

Alex is actually Alexei Zalazof/Biff Slamkovich from Muscle Bomber/Saturday Night Slam Masters.

 * He looks just like him (long blond hair and red headband, even), uses the same moves, and the SNSM Alexei/Biff was an American playing a Russian as part of an Allied Powers tag team with "Guile's brother" Lucky Colt/Gunloc (who was/is Joe from Street Fighter 1). All that would be needed to prove/disprove this would be a simple Word of God.
 * Uh...no. Not the same moves (not even close), taller, bulkier, slower, has not shown any interest in American heavy metal. And all that was ever said about Lucky Colt was that he was "rumored to be related to a famous Street Fighter"; nothing about being anyone's brother, and absolutely nothing at all confirmed. Much more likely explanation is that Alex is just a big wrestling fan who developed his style more or less around the Alexei/Lucky pair.

Necro speaks English as opposed to Russian because...

 * Maybe because Capcom realized they have already fouled Zangief's Russian up? Then how did they brought BOLSHOI TAVIEDA back in CvS2? Capcom Fighting Jam? And his Glorious Mother Russia in his storyline of Street Fighter IV? Will it be a 'mystery' or only his 'trademark'?

Q isn't human, but is instead an extraterrestrial of some kind.

 * Three things: one, out of all the fighters featured in the game, Q is the only one with no home stage of his own (if he's the designated "at-home fighter", the stage seems to be selected randomly); two, between the mask and the rest of his outfit, there's not one square inch of actual skin exposed (nor anything else that'd conclusively identify him as human -- hair, eyes, teeth, and so on); and three, can you honestly tell me after listening to Q's theme music that it isn't a techno remix of the X Files theme music? 5:2 says you can't.

Q is the Slender Man.
He's tall, he never speaks, he doesn't seem to have a face when he's shocked, he appears mysteriously in photos from seemingly unrelated murders, and he can appear anywhere. Need I say more?

Q is Mr. A

 * Hardboiled-stylized? Check. Iron mask? Check. Investigator who isn't afraid to pick up fights? Check. Makes long speeches about Objectivism? Uh, OK, you win here.

Q is Watari from Death Note.

 * Think about Watari's outfit prior to revealing his face. He never spoke, the trenchcoat and hat are the same, and someone had to teach L how to fight.