build/lib/i18n.ts/prepareI18nFiles
export function prepareI18nFiles(): ThroughStream {
	let parsePromises: Promise<ParsedXLF[]>[] = [];

	return through(function (this: ThroughStream, xlf: File) {
		let stream = this;
		let parsePromise = XLF.parse(xlf.contents.toString());
		parsePromises.push(parsePromise);
		parsePromise.then(
			resolvedFiles => {
				resolvedFiles.forEach(file => {
					let translatedFile = createI18nFile(file.originalFilePath, file.messages);
					stream.queue(translatedFile);
				});
			}
		);
	}, function () {
		Promise.all(parsePromises)
			.then(() => { this.queue(null); })
			.catch(reason => { throw new Error(reason); });
	});
}