src/vs/nls.ts/_format
function _format(message: string, args: (string | number | boolean | undefined | null)[]): string {
	let result: string;

	if (args.length === 0) {
		result = message;
	} else {
		result = message.replace(/\{(\d+)\}/g, (match, rest) => {
			const index = rest[0];
			const arg = args[index];
			let result = match;
			if (typeof arg === 'string') {
				result = arg;
			} else if (typeof arg === 'number' || typeof arg === 'boolean' || arg === void 0 || arg === null) {
				result = String(arg);
			}
			return result;
		});
	}

	if (isPseudo) {
		// FF3B and FF3D is the Unicode zenkaku representation for [ and ]
		result = '\uFF3B' + result.replace(/[aouei]/g, '$&$&') + '\uFF3D';
	}

	return result;
}