… however he seems smart enough to realize that if he continues down this road with Trump, he will turn El Salvador into an international pariah and it won't end too well for him.

is party to the Inter-American Court of Human Rights.
And they tend not to fuck around.

I cannot figure why he even cares.
He makes money on the prisoners no matter who they are.

But, history hasn't really been kind to Latin American dictators.
Or most dictators of recent years, to be honest.
The Inter-American Court of Human Rights is quite a robust one and they are not going to let this go, so long as victims file suits and those suits are ignored at the lower court levels. It takes awhile for cases to make their way up that high, but they'll get there.

What power does this court have over those found guilty?

El Salvador sent them back.

Or more afraid of committing human right violations?

I don't see why El Salvador would agree to feed, house and guard this "illegals" for the return of a few criminals. That's a lot of resources they are using that we are not. Would they have a limited holding time? Will these people ever be released? Or killed? What do they plan to do with so many people and with more getting arrested each day?

So he will be pocketing some of this money.

of course they, are didn't we, the law and order party, say so. You can trust use.

in concern for 'due process' or judicial consideration - and a great deal more in strictly administrative process and function. In other words - record keeping - which most (functional) organizations recognize as a desirable end.

How soon those worries might be quelled when millions hang in the balance.