Hi PierreAlainGaltier,
Thanks for your interest in Syncfusion products.
We are unable to reproduce the issue and the added code is sufficient enough to display Legends. Please try to set the visibility of Legends as in below code snippet and check whether the legend is visible or not.
Code Snippet:
legend.Visibility = System.Windows.Visibility.Visible;
If you are still having a problem in displaying Legends, please create a direct track incident regarding this issue. So that we can analyze more on this and provide a better solution.
Thanks,
Rajkumar B R