I modified two strings in the CAS authentication plugin using the Language Customization tool. When I attempted to check the changes into disk, I received the following error:

Coding error detected, it must be fixed by a programmer: Incorrect file location /var/moodledata-2.0/lang/en_local

More information about this error
Stack trace:

line 261 of /admin/report/customlang/locallib.php: coding_exception thrown
line 211 of /admin/report/customlang/locallib.php: call to report_customlang_utils::dump_strings()
line 78 of /admin/report/customlang/index.php: call to report_customlang_utils::checkin()

/var/moodledata-2.0/lang did not exist, so I created it (and the subdirectory en_local) with mode 755 and Apache as the owner. I got the same error, but I notice that the en_local directory was removed by the check in procedure.