The intersting thing is that today's NLP has nothing to do with the manipulation of symbols, as such. Rather, NLP is performed (lately) by neural networks, that learn to optimise the parameters of continuous functions. NLP is possible in this way because by construction, the parameters of the functions to be optimised are associated to the elements of natural language (characters, mostly, but sometimes words). So an NLP "machine" nowadays means a machine that can predict the next character (or word) in a sequence.

Leibniz's ideas on the other hand, of combining symbols to generate and evaluate human language, that's the spirit that permeates Good, Old-Fashioned AI, symbolic, and logic-based artificial intelligence. Today, most NLP researchers would say that the logic-based branch of research, common as it was until very recently, was after all a dead end that did not lead anywhere. It would be interesting to be able to know what Leibniz would have made of that.

Perhaps one day (in the far distant future, when my bones are dust and my memories lost) we'll be able to reproduce the great philosopher's thoughts from his writings and reconstruct his personality, in part or in whole. And then we could pose to him the question: "Master, what do you think of the machine that now houses your intellect"?