code: function getLangDefinition(m) {
          var langKey = (typeof m === 'string') && m ||
                        m && m._lang ||
                        null;
  
          return langKey ? (languages[langKey] || loadLang(langKey)) : moment;
      }
docs: Determines which language definition to use and returns it.  With no parameters, it will return the global language.  If you pass in a language key, such as 'en', it will return the definition for 'en', so long as 'en' has already been loaded using moment.lang.  If you pass in a moment or duration instance, it will decide the language based on that, or default to the global language.