multiple templates for tag pages

This one’s a bit tricky. I would like to enable different templates for displaying the tag pages.
I found the possibility to make custom templates for specific tags. For instance create a tag-NAME_OF_TAG.php page. But that is not practical for thousands of tags.

I only need two classes of templates for tags.
I have two scenarios:

1. The visitor clicks the tag link from a single page that has its own template. Wouldn’t that be nice if tags would be returned in a page that retained that template, instead of the general theme? I can’t imagine the solution, because the link itself its the same, and this couldn’t be achieved without a cookie.

2. The visitor finds the tag page from Google. Some tags refer to articles in English, some refer to articles in other language. (I happen to have different custom functions attached to articles, marking the language of the article.) Wouldn’t it be nice to be able to group tags into two (based on language or on custom function attached to articles)? That way, when a visitor opens an English tag page would be served with the English template also.
I guess what I’m trying to achieve is make tags belong to either a category or a group. I’m not sure if it’s possible.