Export Google Sheets Copy to Json - Apps Script

Code.gs

/* 
Exports a multi-language copy deck into individual JSON files

Expects data in this format

Key   | en      | fr
---------------------------
TITLE | Welcome | Bienvenue

Which exports en.js and fr.json
eg en.js:
{
	"TITLE": "Welcome
}
*/

function exportJSON() {
	const sheet = SpreadsheetApp.getActiveSheet();
	const ui = SpreadsheetApp.getUi();
	const range = sheet.getDataRange();
	const values = range.getValues(); // rows of columms

	// Holds code of language
	const languages = [];
	// Holds objects of keys for each language
	const copy = [];

	values.forEach((row, rowIndex) => {
		// Ignore empty row
		if (!row || !row[0]) return;
		// Use first row to create objects for each language
		if (!rowIndex) {
			row.forEach((value, columnIndex) => {
				// Ignore first column (Key)
				if (!columnIndex) return;
				// Ignore empty cells
				if (!value) return;
				// Create empty object and store language code
				languages[columnIndex - 1] = value;
				copy[columnIndex - 1] = {};
			});
			return;
		}
		// if (rowIndex > 2) return;

		let currentKey = '';
		row.forEach((value, columnIndex) => {
			// Stores each row key from first column
			if (!columnIndex) return (currentKey = value);
			// Adds copy to each language copy object
			copy[columnIndex - 1][currentKey] = value;
		});
	});

	const htmlOutput = HtmlService.createHtmlOutput(
		`
		<script>
			const languages = ${JSON.stringify(languages)};
			const copy = ${JSON.stringify(copy)};

			function timeout(t) {
				return new Promise((resolve) => {
					setTimeout(resolve, t);
				});
			}

			languages.forEach(async (language, i) => {
				await timeout(i * 100);
				const elem = document.createElement('a');
				elem.href = 'data:application/json;charset=utf-8,' + encodeURIComponent(JSON.stringify(copy[i]));
				elem.download = language + '.json';
				elem.click();

				if (i === languages.length - 1) google.script.host.close();
			});
		</script>
		`
	)
		.setWidth(250)
		.setHeight(100);
	ui.showModalDialog(htmlOutput, 'Downloading JSON');
}

Menu.gs

/**
 * Creates a menu entry in the Google Sheets Extensions menu when the document is opened.
 *
 * @param {object} e The event parameter for a simple onOpen trigger.
 */
function onOpen(e) {
	// Builds a menu that displays under the Extensions menu in Sheets.
	SpreadsheetApp.getUi().createAddonMenu().addItem('Export JSON', 'exportJSON').addToUi();
}

/**
 * Runs when the add-on is installed; calls onOpen() to ensure menu creation and
 * any other initializion work is done immediately. This method is only used by
 * the desktop add-on and is never called by the mobile version.
 *
 * @param {object} e The event parameter for a simple onInstall trigger.
 */
function onInstall(e) {
	onOpen(e);
}