I have a player who is a barbarian 5/fighter 5. The barbarian gets extra attack at lvl 5. The fighter does as well.
Does this multiclass combination thus have 3 attacks per round? Or will it have 2 attacks, and only after lvl 11, using fighter 6, have 3 attacks?
Your character will have 2 attacks, and it will take until the 11th level in Fighter (or warrior, depending on your translation) to get a third attack.
This is because of this clause in the Multiclassing Rules:
Extra Attack
If you gain the Extra Attack class feature from more than one class, the features don't add together. You can't make more than two attacks with this feature unless it says you do (as the fighter's version of Extra Attack does). Similarly, the warlock's eldritch invocation Thirsting Blade doesn't give you additional attacks if you also have Extra Attack.
