def language(lang)
      lang ||= :none
      @_stemmer = XapianDb::Repositories::Stemmer.stemmer_for lang
      @_stopper = lang == :none ? nil : XapianDb::Repositories::Stopper.stopper_for(lang)
    end
def language(lang)
      lang ||= :none
      @_stemmer = XapianDb::Repositories::Stemmer.stemmer_for lang
      @_stopper = lang == :none ? nil : XapianDb::Repositories::Stopper.stopper_for(lang)
    end
Set the language.
 @param [Symbol] lang The language; apply the two letter ISO639 code for the language
 @example
   XapianDb::Config.setup do |config|
     config.language :de
   end
 see {LANGUAGE_MAP} for supported languages