Hi there. I don't know what I'm doing when it comes to parenting but thought it might help to share our recent experience.
We have a nearly 2 year old son and a nearly one year old son. Our eldest like yours is slow in terms of language (which is why I came on to post actually). He has routinely been violent with other children, and hasn't responded to any kind of admonishment until very recently (I'm not averse to smacking but cannot see the point in trying to teach a child not be violent by smacking them).
In frustration one of the last times he was violent to his brother, I took him out of the room and put him in his cot. Previously we had determined not to use the cot like a form of gaol, but he usually co-sleeps in with us anyway, and I was at my wit's end.
He hated it. Very very unhappy. I went back in and told him, "Sorry - you've got to stay there. You don't hit your brother."
He remained angry and upset until I took him out and he was a bit clingy. He refused to give his brother a kiss to say sorry, but that's normal.
A few days later he was violent again, and usually I'd either pull him away, and talk sternly to him at some length, or put him in the cot. This time I spoke to him sternly in very few words, but quite sharply too, then I quickly moved on to asking him to give his brother the "sorry" kiss. For the first time ever he voluntarily went over and hugged him and kissed him.
No indication that the two different tactics combined in any way, but each represented an improvement in my mind - the cot seems to serve as a very apparent punishment (and gives you time to console the younger one), and the quick telling-off seemed to do the job but not alienate him so much that he disengaged.