Foriegn markets don't matter too much, because Paramount is not going to get back their losses from foriegn gross. The film is too expensive to worry about releasing it in December to a lukewarm reception and risk potentially franchise-killing box office returns. This way if it's released in May, even if it's as awful as it seems, Paramount can dump enough marketing into it that the frontloaded ticket sales will make 'em bank.
And that's the bottom line. Mediocre movies do mediocre business during winter. But you can make money off of anything released in MAy for the first weekend if you dump enough marketing into it.