We are working with the TaxonomyPlugin. With ‘hippotaxonomy:locales’ we’ve configured the plugin to only use ‘en’ (English). In the editor view this only makes the ‘English’ dropdown available. However when e.g. Dutch editor adds a taxonomy. Also the ‘nl’ key is added and another side effect: this ‘nl’ key is not visible for non-Dutch editors.
I’m trying to figure out now if this is misconfiguration on our part or a bug in the plugin. I’ll keep looking, but maybe you have a quick solution to this issue.
Categories are always linked to a locale. I think it must automatically uses the locale from your session by default. I don’t think this is misconfiguration on your part. As to whether it is a bug…it is a helpful feature which does not match your use case 
Haha thanks…
Do I doubt it’s a helpful feature for anyone, because as an editor once you are under the impression that you’re updating a key in - in this case - the English language. And if you’re logged in as a Dutchie and you set a taxonomy. Select this taxonomy on a document. Later on when an English editor goes to the same document he gets the Dutch taxonomy labels, not the English labels.
There’s something weird about the taxonomy plugin with locales I also noticed. It by default looks at the “Accept-Languge” header sent by the browser. So different people create different language nodes under category nodes. I ended up extending the taxonomyeditorplugin’s getLocale() method .