function getPseudoLanguageTag(sPrivateUse) {
		let sPseudoLanguageTag;
		if ( sPrivateUse ) {
			const m = /-(saptrc|sappsd|saprigi)(?:-|$)/i.exec(sPrivateUse);
			sPseudoLanguageTag = m && "en-US-x-" + m[1].toLowerCase();
		}
		return sPseudoLanguageTag;
	}
Maps wellknown private use extensions to pseudo language tags.
@param {string} sPrivateUse A Locale
@returns {string|undefined} the pseudo language tag or undefined
@private
@since 1.120.0