(Author of the blog post here.) Great question, thanks! Unicode defines six categories of plural forms: zero, one, two, few, many, and other. The names of these categories always appear in English. Unicode also maintains a collection of all mappings of numerical rules to these categories, for all languages supported by the CLDR. See http://www.unicode.org/cldr/charts/latest/supplemental/langu... for the mapping corresponding to the Czech grammar.