Hi Thierry,
I would recommend using a JavaScript function to generate the Tooltip's content. This approach is far more flexible and allows you to get the event's resource(s), then find the matching items in the resource DataSource and display the text representation.
Here is a proof of concept example.
Regards,
Alexander Popov
Telerik
Join us on our journey to create the world's most complete HTML 5 UI Framework -
download Kendo UI now!