When starting an LTI request (via the LtiLibray (https://github.com/andyfmiller/LtiLibrary)) and launch_presentation_locale is set to "nl-BE", the user still gets the Moodle page in English.
Currently using version Moodle 3.2.2+ (Build: 20170316).
Language packs installed: English, Dutch and French.
Language settings: default language = Dutch
Plugins - enrolments - Publish as LTI tool: Preferred language = Dutch
Also when changing the preferred language of the user to Dutch and starting the LTI request again, the preferred language of this user is changed back to English and the page is shown in English.
What parameter should be passed in the LTI request so that the preferred language of the user is correctly set (to Dutch)?