The profile language of a user is French, but if the user opens a diagram, only German-language is shown for the activities:
Image/data in this KBA is from SAP internal systems, sample data, or demo systems. Any resemblance to real data is purely coincidental.
The profile language has no influence on the start language of the diagram, and if you want to adjust the French language, you have to switch it from the main language.
This text purple italic is just a fallback, so you can see, that the current language is not filled out.
KBA , BPI-SIG-CA-MUL , Multi-Language for SAP Signavio , How To