Template for subcategories - via Views?

You don't have to do this. It's already done for you. You can, however, make it better.

Taxonomy already provides such a view for each term at /taxonomy/term/TID (where TID == the term ID). Pathauto will map the URL appropriately to languages/french/grammar if you configure it to use the vocabulary/taxpath, assuming you have arranged your taxonomy terms in a heirarchy.

You're right about not wanting to create 30 views. In general, you don't want to hardcode values into a whole bunch of separate Views if you can pass them as arguments to a common, generalized View. The args can be passed in the URL, or in the case of Views blocks, explicitly by taking advantage of the flexibility provided by the Panels module.

If you want to enhance the page, you could use Panels to override the taxonomy term view, and embed a custom view (to which you would pass an argument), and perhaps custom blocks (which also could be passed arguments).

For example, let's say you want to place a nice synopsis of the category on the top of the page listing the articles. You could use CCK to create a custom content type "catergoryoverview." Write a categoryoverview for each term. Your custom Panels taxonomy page would then pull in the contents of the appropriate categoryoverview node, then display the usual headline/teaser list below it.

We do something like this on our newspaper sites. For example, /sports/basketball would give you a headline+teaser list of all the basketball stories with some enhanced sort options. We have a separate vocabulary for authors, so /authors/joebaloney would give you a similar list of Joe Baloney's stories. But we go beyond that: If displaying an author who has a profile in the system, we pull in a block containing a mini-profile of that author. So /authors/joebaloney would have, at the top, a picture of Joe Baloney, a summary of his background, and a link to his profile page -- followed by the usual headline/teaser list of his stories.