Most German auto insurance companies will accept an original or certified copy of a
recent letter from a non-German insurance company certifying a claims-free record. I've helped a number of friends sort this out. Some will accept faxed or copied letters too (although they shouldn't!). Experience shows they like to know the precise number of years of claims-free driving (so they can drop you easilly into the German system where discounts are measured by years without claim), although some will consider high percentage discounts rates too...
Up to around 10 years ago you could actually buy a no-claims discount from someone else (I bought a 10-year discount one from a guy who had lost his license...), but nowadays that is reserved for transfer of discounts between family members only, so if you have an elderly grandfather with 40 years claims-free driving, who is about to give up (driving!) you can take over his discount... weird, really..

YL6