Hmm, commit 823ebe16 has broken backwards compatability for me 
I had the file:
local/lang/en_utf8/cleo_mis.php
and was using get_string('foo', 'cleo_mis');
From the comments above it looks like moving that file to local/lang/en_utf8_local/cleo_mis.php should work, but it does not.
In lib/locallib.php the comments say:
- Local language support
- ----------------------
*
- Moodle supports looking in the local/ directory for language files.
- You would need to create local/lang/en_utf8/local.php
- and then could call strings like get_string('key', 'local');
- Make sure you don't call the language file something that moodle already has one of,
- stick to local or $clientname)
So that needs fixing if nothing else 
(probably should've tested this earlier since I was watching this issue!)
Attached diff (contains patch from
MDL-13000in part as well as it contains the instructions for implmentation in the lib/locallib.php instructions)MDL-13000in part as well as it contains the instructions for implmentation in the lib/locallib.php instructions)