The answer is very simple. Belgium exists of a Flemish speaking part (Flanders) and a French speaking part (Wallonia). So most Belgian coins exist with a Flemish legend or with a French legend.
Others (like this one) have a bilungual legend with Flemish text first (BELGIË-BELGIQUE) or with French text first (BELGIQUE-BELGIË). That's the difference between KM# 125 and KM# 126. So yours is KM# 126.
To be complete, there is also a small German speaking part in Belgium but there are no coins with a legend only in German. However, there are a few coins with the three languages together on the same coin.