florent6001,

There is no calendar in the left menu in a default MantisBT installation.

This is not a bug or feature request for MantisBT (you are asking for help on how to configure the system). I am therefore resolving this issue as "no change required".

Please use the forums to get support on customizing and using MantisBT (refer to http://www.mantisbt.org/support.php for links and further details).