If we set Moodle to use a package "pt_br_foo", that has parentlanguage set to "pt_br" , and in a custom script i call get_string passing the path to my customscripts lang folder "customscript/lang/" as extra location, the get_string function will not search inside "pt_br" , unless i create a langconfig.php file inside it and set the parentlanguage to "pt_br".

I am attaching a patch (parentlanguage.customscript.diff) that search for the langconfig.php file in the main directory of language (both at dirroot and dataroot) and not at the extralocation directory.