Why don't they talk in "The Red Turtle"

There were some dialogues in the start, but they decided to drop it. It was actually Suzuki’s idea to drop off the dialogues.

What is the cinematic reasoning for a film with no dialogue?

As the director explains in his interview mentioned below, that kinda story can be told without a dialogue and with just expressions.

Cross culturality? Ease of distribution across different language markets?

That can be a reason, but director doesn't mention it.

Director Michael Dudok de Wit explains why "The Red Turtle" has no dialogue. (emphasis mine)

In the beginning, there was dialogue in the script. Not much, just a few lines here and there, very light dialogue between the human characters, because I thought that would fit in naturally and would accentuate our empathy towards them. Also, in two instances, it would explain things a bit, when people really wanted to communicate something. Incidentally, it was clear that the animals in the film would always be real animals, and not humans in animal bodies. Obviously then, the animals would not speak, not even behave like human beings -- one very subtle exception was the little crabs on the beach that behave like crabs, but at some point, appear slightly tamed, a little bit like pets.

I felt strongly about the dialog. But in the animatic, the dialog seemed to fit intellectually, but the feeling was not right. It just felt unnatural. We experimented with different solutions. But it became less and less at some point, and then we just dropped it. It was very much Suzuki’s idea. He was the first one to say, "Why don't we just drop the dialog?" I protested; I said, "I'm not sure it will be clear enough at certain moments for the film." And he said, "We looked at it, and we think it will be clear enough. We think it can be done."

I listened and thought, "Oh damn, this is exciting." I actually really liked the idea of dropping the dialog. Not as a big statement, like "Hey guys, a film without dialogue,” but that a story can be told in a simple way. We know people can talk, but we don't have to see them talk. We see them at moments where they are quiet because they know each other so well, they can communicate just with their behavior and with the expressions on their faces.