Two Handed is better then one Handed, and you can learn the Two Hand Skills only later in the Game.
Its an upgrading for a Warrior, the way to make the Warrior better and better.
In Gothic 2 TNotR you dont need the Two handed Skill. You can find very good one handed weapons. And in G2 TNotR you choose if you find it better to make a strong Charakter or a Charakter with higher dextery.