Error: No localization data in browser console tab

After upgrading to 12.20 track a user may receive in AJAX and in browser's Console tab (Developer tools) the following error:
Error: No localization data

Bookmarks or Report menu instead of values could also not working having an undefined as a value.
Context menu of some object could be empty (right clicking to an object)
Some fields could have value Undefined.
Calendar could not work etc.
 

The root cause is a new feature that has been introduced in 12.20 track, called Switch language, where end users can now choose UI language in the Profile settings in AccessPoint.

If no language is specified, the server should consider English as the default. So, this is currently considered a bug. 

Set environment's default language by adding the following Easter Egg into Settings.ini file InterfaceLanguage=English

• Navigate to the QlikView Management Console - Click on System - Setup - QVS (QlikView Server)
• Stop the QlikView Server Service(s) on the necessary servers, shown in the QMC, and edit the settings.ini which by default is located in the following directory: C:\ProgramData\QlikTech\QlikViewServer
• Add InterfaceLanguage=English in the [Settings 7] section
• Save the file and then restart the service(s).

This will set English as default for all users that don't come via the Access Point or that have not set a specific language preference.