"Erreur de licence - Code d'activation invalide" on Windows 10. Solution: CS6 activation servers are still online, but sometimes blocked by firewalls. Add adobe.com to exceptions or use the telephone activation method (select "Activer par téléphone").
If your CS6 installs in English, you cannot download a language pack. However, you can manually copy the fr_FR locale folder from a working French install. Adobe removed language switching in CS6—you must install the specific regional version. Adobe-Creative-Suite-CS6-Master-Collection-FRENCH
Search for: "Adobe CS6 Master Collection boîte française" . "Erreur de licence - Code d'activation invalide" on
InDesign CS6 crashes when using French autocorrect. Solution: Reset the InDesign preferences: Hold Ctrl+Alt+Shift (Windows) or Cmd+Opt+Ctrl+Shift (Mac) while launching. If your CS6 installs in English, you cannot
This is the trickiest part. Adobe no longer sells CS6 licenses directly. However, for French speakers, there are still legitimate avenues: