How exactly could Michael have gone an entire school year without realizing he was failing French class? Why wouldn't the school inform him? Or his parents? Is it customary to just let students fail unknowingly just to spitefully inform them of their failure the day they graduate?
Also Steranko's evil plan makes no sense. Leaving aside the unlikelihood that he could take over Europe just by poisoning a few heads of state and expect to step into their collective shoes without any opposition, he's really counting his chickens before they hatch by stealing gold to mint coins for his own country that doesn't even exist yet.
Mrs. Grober: [meekly protesting their kidnapping] Look, this is all very fascinating, I'm sure, but, um, this is simply not on the schedule! You see, we were supposed to be in Dijon this morning. You understand? Mustard land! And - and last night we were supposed to be in a castle in Strasbourg... Zigesfeld: [losing his temper finally] Shut up, you whining bitch!
Although the immediate problem of the villain is handled by the film's climax, there's the somewhat major issue of all the gold he stole from France, Germany and other European countries and melted down. Namely, that it was in his mansion when it exploded. There's a strong possibility that Europe could suffer economic crises as a result.
There is also the matter of the "other" Michael Corben and what will happen to our young hero when his true identity is found out. The movie ends with him basically implying he isn't the Corben they thought all along. When (and if) it is eventually discovered that the real Agent Corben was killed in Detroit, Michael could potentially face serious consequences for willfully duping the intelligence agencies of no less than three different countries. Most likely they'll offer him a job since this is Martini-flavored spycraft.
Unintentional Period Piece: The villain's evil plan is to establish... The Euro, which came into being for real less than a decade after the film was released. Thankfully, without the need to murder people who disagreed with it's establishment, but with clear signs that his plan wouldn't have worked in the long run. Hilarious in Hindsight if you're not in the European Monetary Union. ...Of course, if you are...