code.gs

/**
 *
 * OnInstall method.
 *
 * Necessary for the menu items to populate the first time after the add-on is installed.
 *
 **/
function onInstall(e) {
    onOpen(e);
}

/**
 *
 * Toolbar menu creation.
 *
 * Called on worbook opening.
 *
 **/
function onOpen() {
    SpreadsheetApp.getUi()
        .createAddonMenu()
        .addItem('Start a new translation', 'showSidebar')
        .addItem('About', 'showAbout')
        .addToUi();
}

/*
 * Example function for Google Analytics Measurement Protocol.
 * @param {string} tid Tracking ID / Web Property ID
 * @param {string} url Document location URL
 */
function sendGAMP(tid, url) {
    var data = {
        'v': '1',
        'tid': tid,
        'cid': Utilities.getUuid(),
        'z': Math.floor(Math.random() * 10E7),
        't': 'pageview',
        'dl': url
    };
    var payload = Object.keys(data).map(function(key) {
        return encodeURIComponent(key) + '=' + encodeURIComponent(data[key]);
    }).join('&');
    var options = {
        'method': 'POST',
        'payload': payload
    };

    UrlFetchApp.fetch('http://www.google-analytics.com/collect', options);
}

/**
 *
 * Sidebar title, content & size.
 *
 **/
function showSidebar() {
    var html = HtmlService.createHtmlOutputFromFile('index')
        .setSandboxMode(HtmlService.SandboxMode.IFRAME)
        .setTitle('Translate My Sheet')
        .setWidth(300);

    // Open sidebar
    SpreadsheetApp.getUi().showSidebar(html);
}

function showAbout() {
    var html = HtmlService.createHtmlOutputFromFile('about')
        .setSandboxMode(HtmlService.SandboxMode.IFRAME)
        .setTitle('About')
        .setWidth(250)
        .setHeight(450);
    SpreadsheetApp.getActive().show(html);
}

/**
 *
 * Translate function.
 *
 **/
function translate(radioFull, radioSelected, radioOgSheet, radioNewSheet, sourceLangage, targetLangage) {
    var activeSpreadsheet = SpreadsheetApp.getActiveSpreadsheet();
    var activeSheet = activeSpreadsheet.getActiveSheet();
    var activeRange = activeSheet.getActiveRange().getA1Notation();
    activeSpreadsheet.toast("Translation in progress...", "", -1);
    try {
        if (radioOgSheet) {
            var targetSheet = activeSheet
        } else if (radioNewSheet) {
            var newName = activeSheet.getName() + " - " + targetLangage;
            if (activeSpreadsheet.getSheetByName(newName)) {
                var sheets = activeSpreadsheet.getSheets();
                var counter = 1;
                for (var i = 0; i < sheets.length; i++) {
                    if (sheets[i].getName().indexOf(newName) != -1) {
                        counter++;
                    }
                }
                newName += counter;
            }
            var targetSheet = activeSpreadsheet.duplicateActiveSheet().setName(newName);
            targetSheet.setTabColor("1E824C");
        }
        var activeCell = activeSheet.getActiveCell();
        if (radioFull) {
            translateFullPage(targetSheet, sourceLangage, targetLangage);
        } else if (radioSelected) {
            translateSelectedCells(targetSheet, activeRange, sourceLangage, targetLangage);
        }
        activeSpreadsheet.toast("Done.", "", 3);
    } catch (err) {
        activeSpreadsheet.toast("An error occured:" + err);
    }
}

/**
 *
 * Code for translate full page content from a source to a target langage. 
 *
 **/
function translateFullPage(targetSheet, sourceLangage, targetLangage) {
    var lrow = targetSheet.getLastRow();
    var lcol = targetSheet.getLastColumn();
    for (var i = 1; i <= lrow; i++) {
        for (var j = 1; j <= lcol; j++) {
            if (targetSheet.getRange(i, j).getValue() != "") {
                var activeCellText = targetSheet.getRange(i, j).getValue();
                // TODO: here, wrap the call in a try catch
                var activeCellTranslation = LanguageApp.translate(activeCellText, sourceLangage, targetLangage);
                targetSheet.getRange(i, j).setValue(activeCellTranslation);
            }
        }
    }
}

/**
 *
 * Code for translate only selected range content in a sheet from a source to a target langage. 
 *
 **/
function translateSelectedCells(targetSheet, activeRange, sourceLangage, targetLangage) {
    var range = targetSheet.getRange(activeRange);
    var numRows = range.getNumRows();
    var numCols = range.getNumColumns();
    for (var i = 1; i <= numRows; i++) {
        for (var j = 1; j <= numCols; j++) {
            var activeCellText = range.getCell(i, j).getValue();
            // TODO: here, wrap the call in a try catch
            var activeCellTranslation = LanguageApp.translate(activeCellText, sourceLangage, targetLangage);
            range.getCell(i, j).setValue(activeCellTranslation);
            range.getCell(i, j).setBackground("#1E824C");
            range.getCell(i, j).setFontColor("#FFFFFF");
        }
    }
}