We apologize for the inconvenience caused, Is the language change is only with Acrobat Pro DC or with other Adobe apps too?
Try uninstalling Acrobat using the Acrobat cleaner tool Download Adobe Reader and Acrobat Cleaner Tool - Adobe Labs Reboot the machine and install Acrobat from Download Pro or Standard versions of Acrobat DC | Non-subscription
Have you tried changing the language from Creative Cloud desktop app? To change the language preferences, please refer to Change the language setting of your Creative Cloud apps
If the issue still persists, please create a test user profile with full administrative rights or enable the root account of the Mac OS and check with Acrobat and see if this issue is reproducible?
Let us know how it goes and share your findings.
I had tried using the Adobe Creative Cloud Cleaner Tool, but it didn't have an option to clean Acrobat.
I used the specific Adobe Reader and Acrobat Cleaner Tool and then installed the Acrobat Pro Classic 2015 version downloaded from the link above. That fixed the issue with the Japanese characters displaying in the Help drop down menu and alert boxes.
I then reinstalled the latest Acrobat DC version from the Desktop CC app and it also works perfectly with no Japanese glitches.
Thanks for the help! ;-)
Great! Good to hear that the issue got fixed, nice job troubleshooting that. Feel free to update this discussion for any further query.