code: function getLangDefinition(key) {
          if (!key) {
              return moment.fn._lang;
          }
          if (!languages[key] && hasModule) {
              try {
                  require('./lang/' + key);
              } catch (e) {
                  // call with no params to set to default
                  return moment.fn._lang;
              }
          }
          return languages[key];
      }
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.