Best practices concerning native language and noise

Hello, I recently started using Obsidian and informed me with the LYT videos and “taking smart notes” by Ahrens.

Now i have some questions:

Not sure in which language my “Zettelkasten” should be. German is my native language, but most of my literature I read is in English. So, every time I read something, I must translate it to German, but that would be even better than just rewrite it in my own words, right?

Another question is regarding noise: in my feeling, all notes I produce from literature are too near to the cited literature. How do you reduce noise in your notes or how do you get the feeling that the note only contains the necessary?

I am processing my literature with Zotero an export them with Mdnotes, but how do you work through your highlights and notes exactly? Currently I am reading them again and trying to generate permanent notes from them.

Thank you very much and kind regards