build/lib/i18n.ts/XLF/addStringItem
class XLF:	private addStringItem(file: string, item: Item): void {
		if (!item.id || item.message === undefined || item.message === null) {
			throw new Error(`No item ID or value specified: ${JSON.stringify(item)}. File: ${file}`);
		}
		if (item.message.length === 0) {
			log(`Item with id ${item.id} in file ${file} has an empty message.`);
		}

		this.appendNewLine(`<trans-unit id="${item.id}">`, 4);
		this.appendNewLine(`<source xml:lang="en">${item.message}</source>`, 6);

		if (item.comment) {
			this.appendNewLine(`<note>${item.comment}</note>`, 6);
		}

		this.appendNewLine('</trans-unit>', 4);
	}