Hi Stephane,
There were some issue related to the DictionaryPath in C1Editor in the previous version. Please download the latest build from http://prerelease.componentone.com/dotnet30/c1webwijmo.webforms/2013-t2/C1WebWijmo.Webforms_3.5.20132.129.zip which fixed the issue.
You may use the french dictionary (C1Spell_fr-CA.dct) at the following location on your machine :
C:\Users\\Documents\ComponentOne Samples\Studio for Silverlight\General\CS\ControlExplorerOld\ControlExplorerWeb
Regards
Abdias