I updated the link in the Ask the Expert post, but here is the link to the demo project: https://www.filehosting.org/file/details/761573/LanguageSwitchTest.mpk
Hope that helps,
See this forum post, it might help: https://forum.mendix.com/link/questions/85498
In februarys webinar "Ask the Expert" Mike Kumpf created a test project for this and he explains how he did it in that webinar: https://ww2.mendix.com/cw-ask-the-expert.html.
Perhaps this will help you as well. I was not able to download the sample project, but perhaps Mike still has that available for you?