Returns the CLDR data for a given locale
@param locale {String} the locale string
@returns Promise({cldr})
async function(locale) {
      var t = this;
      var cldr = this.__cldrs[locale];
      if (cldr) {
        return cldr; 
      }
      return qx.tool.compiler.app.Cldr.loadCLDR(locale)
        .then(cldr => t.__cldrs[locale] = cldr);
    }