
As JG says, take the dog to the vets, I don't think language will be too much of a barrier, if a vet is presented with a sick dog they will know if it is serious or not. I'd be inclined to think the climate is too hot for him so may need keeping indoors or in the shade when outside, but not walking in that heat.
Too much sea water can be a problem if the dogs drink it, I am not sure what it can do but saw a post somewhere on this forum (I think) not too long ago about the dangers of sea water.
Definitley off to the vets is my opinion.