The language filter works as expected. My problem however is that the banner show up in *all* posts. I need it to display only in the posts with the specified categories.
Remember that you can debug a conditional shortcode by adding the debug="true" argument. This will display information about the conditional for administrators, which will help you find out what's going on.
I hope this helps. Otherwise, please allow me temporary access, and provide the link to the content template and let me check it further. Your next reply will be private to let you share credentials safely. ** Make a database backup before sharing credentials. **