In the first time when we migrated to wordpress for the Fellowship blogs I was a bit confused about the difference between categories and tags. And when I talked to Fellows they are also a bit unsure about that. So I read a bit more about it, especially a blog post about "categories vs. tags" to find a good solution.
And here it is: As I will also blog in German from time to time my conclusion from this article was to use categories only for languages; so I have the categories "English" and "Deutsch". For the rest I will use tags, as they can be added faster than categories. E.g. I tagged this message with "infrastructure, wordpress, blog".
The nice thing is, you have RSS feeds for categories as well as for tags... E.g. the category "Deutsch" is "?cat=708" on my blog (if you use another option it is possible that it is "/deutsch"). So to get a RSS feed with only the blog entries from the German category you can add the category name this way to the feed URL so you have "http://blogs.fsfe.org/mk/?feed=rss2&cat=708". That is it. Blog about Free Software using Free Software :-) .