Some reasons why it's ideal to translate your tags or categorizations:
- Tag labels presented to users won't be understandable in another language. If your company is a German rail equipment manufacturer, you shouldn't expect an American to understand "Straßenbahnsignalsystem", nor should an American manufacturer expect others to understand "Light rail signaling system".
- Tag "slugs" or URI segments (e.g. /news/category/health) should be translated for better SEO performance, helping your users find your content (e.g. /nouvelles/categorie/sante in French).
Note that you may not need to map tags one-to-one between your languages or locales. If your tags are specific to a market it may not make sense to have them in another market.
Another thought... Having parts of your interface untranslated may create a jarring experience for your user. If you're not in the position to tag in all of your different locales, consider only tagging those where you can. It might make more sense to not offer a functionality than to create a confusing or frustrating experience.