Combining suggestions from all sides, what we seem to be proposing is either a new section in the general settings for a group, or maybe a new tab on the group's settings page.
CATEGORIES -- Select up to 3*
[Drop-down list of agreed categories]
SUBJECT TAGS -- Provide up to 5**
[User-identified topic tags]
LOCATION -- Add as appropriate
LANGUAGE(S) -- Select as many an necessary
[Standard drop-down list of languages]
*The drop-down list might contain just the label for the category, but elsewhere -- perhaps in the wiki, perhaps somewhere else -- there would be a document that develops the idea of each category without actually naming each and every possible subcategory. Something along the lines of:
Entertainment and Performance Arts. Includes groups that discuss such topics as TV, Radio, Movies, Books and Authors, Theatre.
Family and Home. Includes groups that discuss topics such as Gardening, Genealogy, Parenting, Home buying/selling, Pets, (maybe Alternative Housing Arrangements to satisfy Sharon?)
Medicine, Health, and Wellness. Includes groups that discuss such topics as Fitness, Nutrition, Support for people experiencing specific medical issues.
Music and Musicians. Includes groups that discuss all genres and time periods of music (e.g. Early Music, Classical, Country, Pop, Rock) as well as performers and performances (live, recorded, streamed, videos, etc).
Obviously, this would need some work to develop it into a clear and comprehensive document. But the idea is that is would be suggestive rather than prescriptive.
**Tag management would still be an issue, but perhaps there could be an advisory document for that as well, giving advice to owners such as:
Use "amateur radio" rather than "ham radio".
Beware of usage differences in other parts of the world. For example, use both "railroads" and "railways" to cover both the U.S.-used term and that used by the rest of the world.
Consider what words you've used in your group's description. If you used PTA in the description, use "Parent Teacher Association" in your tag.
This set of descriptors allows owners to provide meaningful descriptions of their groups for a potential world-wide audience. And (rashly assuming a willingness by Mark to do the coding :-)) for multi-element searching to combine categories with tags with keywords from the groups' descriptions, and possibly even location and language.