Hi Irena,
It's good to hear from you!
What way are you anticipating his dysgraphia and dyspraxia will cause issues with learning a foreign language? FWIW, our ds hasn't had any issues at all with learning Spanish - he uses his regular accommodations (keyboarding, extended time, etc) and he's done quite well with it, hopes to continue to study it at college and possibly use it in business someday. His Spanish classes have been interesting too because he's learned a lot about different cultures around the world.
FWIW, I think sign language wouldn't work for my ds due to his fine motor issues.
I have heard of people getting exemptions from foreign language for students who need them through their IEPs... but I'd also consider looking at what colleges require as sanne mentioned. I've lost track of what grade your ds is in - will he be in high school year after next or middle school? If he's in middle school now, that might be the place to try out a foreign language course as an elective, and if it doesn't go well advocate to replace it with something else in high school.
Best wishes,
polarbear
