In some ways, the language of the video doesn't matter. Answers on the main site should be self-contained. That is, if you read the text of the answer but don't follow any of the links, that should be enough to know the answer to the question. Any videos or other links in the answer should just be to illustrate it with examples.
If you think of it in that way, if the example in an answer is a video, it doesn't matter what people say in the video, because the music is the important part. Whatever is said in the video should already be covered by the text in the answer. In that case, it doesn't matter if the people in the video speak German or any other language, because you don't need to understand what they say to understand the answer.
Any answer where the content of the answer is on the other side of a link, or you can't understand the answer at all without watching the video, may be flagged and deleted as a "link-only answer". The purpose of this site isn't to make a collection of links like a search engine, it's to make a collection of genuine questions and answers. If your aim is to make the videos easier to find or more accessible, this isn't the place to do that. Instead, you might make a post on your blog or on a forum for beginning musicians.