Fatal error when changing the default admin language to a non installed language

Overview of the issue

When setting the admin language to a non-active language, WPML String Translation may throw a fatal error.

Example:

Activate WPML with only “English” as default language, and “Italian” other language
In WPML->Languages select French as default admin language
You get either a white page or a message showing the fatal error

The next version of String Translation will contain the fix to this issue.

Meanwhile, you can follow the following steps to fix it in your installation.

Before doing that, make sure to make a copy of the edited file before editing it, and a backup of your site.

Change the whole function from this:

function init_active_languages() {
   global $sitepress;
   $this->active_languages = array_keys( $sitepress->get_active_languages() );
}

To that:

function init_active_languages() {
   $this->active_languages = array_keys( $this->sitepress->get_languages() );
}