In my experience, researchers who have not had English as their medium of instruction prefer reading articles in their native language. Some find it tedious to navigate research papers in English, especially the ones that are jargon-heavy. Many end up using Google translate!
By publishing your article in German, not only will you be targeting this niche but also doing them great service. But, to target a wider audience, you can just as easily have your manuscript translated by employing machine translation services for a nominal charge or even for free. Read more on this here: https://www.researchgate.net/institution/Peerwith_Connecting_Experts/post/5bd1928336d235276419b55d_Peerwith-peer-2-peer_researcher_services_platform.
Alternatively, you can prepare an English version of your manuscript and have it edited by a subject expert. See: https://www.researchgate.net/institution/Peerwith_Connecting_Experts/post/5bf52e220f95f19d9f3ce50a_For_clients_and_experts_Why_Peerwith.
Many journals (that publish in English) these days support the republication of manuscripts that have already been published in another language. The only condition they impose: Full disclosure and a copy of the previous publication.