Thanks to jacob from the support team.
Renaming the local language folder  (FR-fr to FR-fr---whatever) seems to have trick P&ID errors: C:\Program Files\Autodesk\Revit 2018\AddIns\PnIDModeler
 
 
here is the full reply I got:
 
Hi Jean-Marc,
Thank you for letting me know, 
We've had similar reports recently, and are trying to find one fix for it all without having to wait for a service rollout. Could you try and rename the language folder under “C:\Program Files\Autodesk\Revit 2018\AddIns\PnIDModeler“ which is its default path.
E.g. for French rename “fr-FR“folder for German to “fr-FR--”, and you will get the English version of P&ID modeler. 
Please let me know if it gets rid of the P&ID modeller error, 
 
Best regards,
Jacob Westergaard
Autodesk Support Team