Attached here is a zip folder. Download it to your computer, then extract the file it contains (“I18N.php”) to your computer,. Then upload that file to the kiwitrees installation on your web server. Put it in the folder “kiwitrees/library/KT/”, replacing the file of the same name that is already there.
You should now be able to complete the setup. It will no longer matter of APC, or APCu exist, or if they are enabled or not.