Regarding word games with ability difference - we had the same issue in my group of gamer friends, so we experimented with some handicapping, which we found could work quite well.
The game we particularly like is bananagrams (and I guess you could make your own version on little squares of paper for free, or use a scrabble set if you have one, though the letter frequency might be different). Bananagrams is kind of like free-form speed scrabble, but way more fun than scrabble!
Some constraints we placed on the better player only to make the game more even:
* Only allowed to use themed words (super hard, but fun)
* Not allowed any two-letter words (even on crossover words) - this was our favourite in the end; balanced well
* Only allowed odd numbers of letters
* Not allowed to used plurals or verb forms
* Only allowed words of a certain length, say 4 letters (super hard)
* Some combination of the above
For your situation, have you tried playing word games in either his language, or where you are both allowed to use your first language (this would work fine for bananagrams)?