That neither region, nor site:de helps in getting German *language* results. You'll get "Germany" results.

It would be useful to have a region setting similar to Latin America (xl-es) for German speaking countries, (e.g. xl-de := de-de OR at-de OR ch-de).
posted by <hidden> • 1 year and 8 months ago Link

kl=de-de should work for you, example:
posted by x.15a2 Community Leader1 year and 8 months ago Link