Basically the title. Beyond the Mexica and the Tlaxcalans, what other groups spoke Nahuatl - and what was the (estimated) total population of speakers across Mesoamerica?
Langauges in the same family as Nahuatl predominated across what would now be central Mexico. Getting numbers for the speakers of those langauges is at this point very difficult to the point of impossibility, due to two factors:
Since many of these smaller languages and dialects have been lost due to population decline, it would be hard to determine how many people spoke Nahuatl as we understand it.
More importantly, preconquest population in general is a highly contested question, making questions about subsets of those numbers even more difficult.