static checkDuplicateTimezoneNames(sCLDRTag, oTimezoneNames) {
		// ensure city names are unique to be able to uniquely format/parse them
		const aTimezoneNames = Timezones.getAllChildValues(oTimezoneNames);
		const aDuplicateTimezoneNames = aTimezoneNames.filter((sTimezoneName, iIndex) => {
			return aTimezoneNames.indexOf(sTimezoneName) !== iIndex;
		});
		if (aDuplicateTimezoneNames.length) {
			throw new Error("'" + sCLDRTag + "' contains duplicate time zone names: "
				+ aDuplicateTimezoneNames.join(", "));
		}
	}
Checks whether all time zone names are unique.

@param {string} sCLDRTag
  The language tag as defined by the IETF BCP 47, e.g. "en", "de-CH" or "sr-Latn"
@param {Object<string, object>} oTimezoneNames
  The resulting <code>timezoneNames</code> object of the currently processed locale in which the missing
  time zone names are set
@throws {Error}
  If there are duplicate time zone names.