build/lib/i18n.ts/XLF/toString
class XLF:	public toString(): string {
		this.appendHeader();

		const files = Object.keys(this.files).sort();
		for (const file of files) {
			this.appendNewLine(`<file original="${file}" source-language="en" datatype="plaintext"><body>`, 2);
			const items = this.files[file].sort((a: Item, b: Item) => {
				return a.id < b.id ? -1 : a.id > b.id ? 1 : 0;
			});
			for (const item of items) {
				this.addStringItem(file, item);
			}
			this.appendNewLine('</body></file>');
		}
		this.appendFooter();
		return this.buffer.join('\r\n');
	}