A nice dream.

First reason : Having a common European army means having a common European foreign policy. Uh uh - yeah, just come back in one or two centuries, maybe we'll be able to see the possibility of an agreement on the colour of the uniforms by then.

Second reason : language.

I remember that cartoon I saw in a Belgian newspaper :

A French Officer tries to train a German soldier.

    Officer : "Alors maintenant que vous avez dégoupillé la grenade, vous comptez jusqu'à 10 et vous la lancez.." (Ok, so, now you've pulled the pin of that grenade, you count up to ten and you launch it...")

    Soldier : "Vertater !" (Translater !)