testGetRegionSubTag() {
    let result = locale.getRegionSubTag('de-CH');
    assertEquals('CH', result);

    result = locale.getRegionSubTag('de-latn-CH');
    assertEquals('CH', result);

    result = locale.getRegionSubTag('de_latn_CH');
    assertEquals('CH', result);

    result = locale.getRegionSubTag('de-CH-xxx');
    assertEquals('CH', result);

    result = locale.getRegionSubTag('de-latn-CH-xxx');
    assertEquals('CH', result);

    result = locale.getRegionSubTag('es-latn-419-xxx');
    assertEquals('419', result);

    result = locale.getRegionSubTag('es_latn_419_xxx');
    assertEquals('419', result);

    // No region sub tag present
    result = locale.getRegionSubTag('de');
    assertEquals('', result);
  }
Valid combination of sub tags:
 1)  LanguageSubtag'-'RegionSubtag
 2)  LanguageSubtag'-'ScriptSubtag'-'RegionSubtag
 3)  LanguageSubtag'-'RegionSubtag'-'VariantSubtag
 4)  LanguageSubtag'-'ScriptSubTag'-'RegionSubtag'-'VariantSubtag