It's strange... I learned French years ago and numbers were the first thing they taught us. Why haven't we learned it yet? I can't seem to find it on my Skill Tree (Of course, my powers of observation aren't my best feature.)
It is on the skill tree, it is in the second last area and the second row from that check point. :) the picture/icon for that unit is numbers. (I apologize I suck at explaining where it is located but if you check again you'll see it)
Edit: It is on the 16th row of skills from the bottom.
I hope this helped. ^w^
The numbers in French are very important to know and they are hard to lern. Every language course is obviously created differently and they focussed on providing other knowledge first - this is totally okay to me. If you want to learn the numbers earlier, please have a look here: http://french.about.com/library/begin/bl-numbers.htm