The new Japanese trailer for Joss Whedon’s Avengers includes some footage not included in previous trailers including a glimpse of the alien invasion, dialogue from Maria Hill (Cobie Smulders) and Hawkeye.  Joss Whedon’s Avengers, which many analysts have predicted will be a big hit (see "How Big Will the Avengers Be?"), opens on May 4th.
As for those aliens, well Whedon maintains that they are not the long-rumored Skrulls (see "Whedon Confirms No Kree or Skrulls"). Compare the Japanese trailer with the most recently released American trailer (see "New 'Avengers' Trailer") to see the difference.