Guild Wars 2

Master trait in Wilderness Survival. Off hand training. Decreases cool down and increases range for all off hands.

In addition to Off-Hand Training recharge and range, the damage bonuses are flat. So while a warrior does 5% more damage while wielding an offhand axe, that affects his main hand as well. When a ranger does 10% more damage when his endurance is full, that applies to the warhorn.

Edit: Since the topic is now confusing, the OP was asking about improving offhand weapons.