There was one migrant crisis during the Obama years IIRC where it was some obscure native South American Tribe that tried to cross the border illegally, like hundreds of them, and it took an anthropologist to figure out just how to communicate with that group.
Trump is fucking up the story but there's actually an element of truth here. Border patrol likely told him the story to describe the day-to-day of a border patrol agent, and then Trump misunderstood and is now telling this... New thing... But anyone who knows the border knows the nugget of truth here.
It's like when that Senator said: internet is a series of tubes (instead of pipes, because pipe is ACTUALLY a computer networking term). It's a reasonable mistake for a non-technical policy maker to say here.
Trump says a lot of shit. But this one about not understanding some languages of some migrants... Yeah, it happens every few years. There's a lot of random native American tribes who don't speak Spanish, English, or Portuguese.