Can I use getActiveUserLocale() in onOpen(e) of a published Add-on?

Question

Google shows at https://developers.google.com/apps-script/reference/base/session#getactiveuserlocale how to get the Locale for the active user.

I have an editor (not G-Suite) add-on that I want to make multilingual so that when the user opens the Sheet, which triggers the onOpen(e) function, the Add-on checks the user's locale and then translates the Add-on into the user's language.

Questions:

1. Can I do this in order to translate the menu into other languages?

function onInstall(e) {
  onOpen();
}
function onOpen(e) {
  var lang = Session.getActiveUserLocale().split("_")[0];
  if (lang === 'en'){
  SpreadsheetApp.getUi().createMenu('test')
  .addItem('Publish', 'upload')
  .addToUi();
  }
  else{
  SpreadsheetApp.getUi().createMenu('test')
  .addItem(LanguageApp.translate('Publish posts','en',lang), 'uploadPosts') 
  .addToUi();
  } 
}

2. Do I need to add the Locale scope: https://www.googleapis.com/auth/script.locale to my manifest file as well? When I published the Add-on without the scope, users were seeing a blank menu dropdown.
3. If I do need the scope, why isn't documented at https://developers.google.com/apps-script/reference/base/session#getactiveuserlocale.

Answer 1

The documentation doesn't mention that an authorization scope is required, so Session.getActiveUserLocale() can be called from onOpen.

---

As this is about the onOpen simple trigger on Google Apps Script add-on you should be aware about the add-on authorization live-cycle.

Basically you should consider the following cases

1. Users who have installed the add-on on spreadsheets where the addon hasn't being enabled (authMode = NONE)
2. Users who have installed the add-on on spreadsheets where the addon has being enabled (authmode = LIMITED)
3. Users that are editors of an spreadsheet where the addon has being enable but who haven't installed it (authmode = LIMITED but the user have not authorized the script to be executed)
4. onOpen being called by the active users (authMode = FULL)