Then one have to change the permalink for all the documents once the slug changed. I’d prefer to set the permalink in the config file for the site. Since the slug will be the same for all the documents.
You can’t change the permalink for terms. I suggest using the slug-name of the term you want to use in the URL, and add the translated name to the term’s front matter, so it shows in term lists and and that page as the appropriate name.
Or don’t worry about it. I think it’s fine using those in URLs. Humans won’t mind.
You don’t want tags/目録/. What do you want that to be instead? If you wanted it to be tags/example/, when you add the tag to the content, you would write:
---
title:xxx
tags:["example"]
---
And in content/tags/example/_index.md:
---
title: 目録
---
That would give the tag (rendered at example.com/tags/example) the correct title. That is the only option I know of, currently.