4 cops should have the training to restrain one man.
Whilst he appeared agitated, he did not appear hostile in a life threatening manner.
Also the knowleedge that he cannot understand English, should give you a clue as to why saying things like calm down may not have much response, after the first taser shot the fact that he becomes more agitated is not a suprise.
Note even then it was not by making threatening moves towards the police like a drug crazed homicidal maniac but just reacting to being tasered, training should allow you to asses this situation and the reactions to it quick enough to realise this, otherwise your training is lacking.
The problem is tasers are percieved and marketed as non lethal so its becomes an easy way out with the perception its not really going to do much damage so its a good option.
Taser training should be on a response level just below guns, i.e somewhere near last resort when the threat is to great to try any other methods.