ORA-12705: Cannot access NLS data files or invalid environment specified

I was trying to use TOAD to connect to Oracle DB. Normally I use SQLDeveloper. I understand TOAD is more powerful, but I don't like its UI and I have only the FREE version.
Here it suggests to run regedit and rename NLS_LANG into NLS_LANG_X under any occurrence of the key in HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE. I found several occurrences and replaced them all.

It didn't work.


Then I tried changing the Oracle Installed Client to XE and it worked

See also http://www.dba-oracle.com/t_ora_12705_resolution.htm
All this royally sucks. Meaningless error message without any context information.
Anyway I wanted to run TOAD for the "data compare" diff utility between 2 schemas, but it's available only in the commercial version.