The weapon skill levels, and the class skill level are two different things you have to train. When you reach to level ten of a weapon skill tree, you can use that weapon for any other class, if you switch at the Dhrama Shrine or Alltrades Abbey. Any spells or skills you learn in one class can be used in any other class, as long as you have the correct weapon to use it with. It takes a certain amount of words, to level up for weapons and classes, and you can't train both at the same time, you have to focus on one until you level up, then focus on another.
Skill Level experience needed for Weapons
Level One- 200 Words
Level Two- 350 Words
Level Three- 600 Words
Level Four- 700 Words
Level Five- 800 Words
Level Six- 950 Words
Level Seven- 1150
Level Eight- 1300
Level Nine- 1450
Level Ten- 1600
Skill Level Experience for classes
Level One- 250
Level Two- 450
Level Three- 650
Level Four- 900
Level Five-1100
Level Six- 1350
Level Seven- 1500
Level Eight- 1750
Level Nine- 2000
Level Ten- 2250