Why we don't say "one naira, two nairas"

TELAWAA: Thursday, February 11, 2016

 Have you ever stopped to ask why we say "One dollar, two dollars, 50 dollars...; one pound, two pounds, 50 pounds..." but we say "One naira, two naira, 50 naira...? Shouldn't it be "two nairas, fifty nairas, just as we have "two dollars, fifty dollars...; two pounds, 50 pounds...? Why so? Truth is that, characteristically, every language is conventional, meaning that it first has to do with the perception of the early users of the language. You can't tell exactly why early users chose to avoid the plural marker "s" in the word "naira". To start with, is the word "naira" an English word? I think no! So, do we expect to go by the 's' plural marker which is English? How I wish someone gets my point!