I would assume that you click on Buy instead of Continue Tryout in the message that you get each day of the 30 day tryout.
Is there a problem in doing that? Or it is that the tryout version is in one language and you want to purchase the program
with a different language than the tryout? What language did you set for the tryout? Did you have a choice for French at that time?
According to the Adobe web site Premiere Elements 13 download page
System requirements and supported languages:
Get the full list of system requirements here. The trial is currently available in English, French, German, and Japanese for Microsoft Windows and Mac OS. Additional language versions for Windows are also available.
I would contact Adobe Sales to confirm the details of what you have before you make the actual purchase transaction.