Adobe Acrobat XI Pro - French language pack

@benoitduQC Whoa...what's with all the older questions on the older software?! Adobe Acrobat XI Pro. You cannot use language packs for the Adobe Acrobat XI Pro application in the same way you would with a Creative Cloud subscription. Adobe Acrobat XI Pro is an older, discontinued app (support ended in October 2017), and its language handling is fundamentally different from a subscription-based app. If I remembered correctly, you had the choice of language when you bought the licenses back in the day.

For example, you have a North American English version, that's what your license entitles you to use, regardless of what you try to change in the preferences. The software will detect the discrepancy and revert to its licensed language. If this was the Fench version, then it would be no problem (but it won't open as English).  Try going to the Control Panel > Programs and Features, find Adobe Acrobat XI Pro, and click Change. You may see an option to modify the installation and add a different language. However, this only works if your original installer was a "Multi-Language User Interface" (MUI) version. If that doesn't work, hold down the Ctrl key on your keyboard while launching the Acrobat application. This may prompt a pop-up window asking you to choose a language from a list of those installed on your system. Again, this only works if the French language files are present on your computer.

If you want a French interface, you need to upgrade, https://www.adobe.com/acrobat/pricing/compare-versions.html