You can set the preferred language for the local help files in the help client - independently from the programs.
Which help client are you reffering to? If I select F1 or any help topic in AEs help menu my browser opens up http://helpx.adobe.com/de/after-effects/topics.html if I deactivate ae_force_english. If I switch to english my browser isn't getting any request (only update, adobe id and deactivate aren't translated and actually open up in firefox). The closest thing to a help client I have found is the Help.exe in C:\Program Files (x86)\Adobe\Adobe Help but I found no way to select a language and there also seems to be no local helpfiles because if I select "Only local helpfiles" even the german UI doesn't load or show any help.
Simple solution: go to "Help" then "Welcome and Tip of the Day..." in the next window choose "Help and Support" For this action, you need a internet connection.