Comment 69 for bug 10910

No, the whole purpose of LC_ALL is to allow you to override everything else, whereas the purpose of LANG is to provide the lowest-priority default. The more specific LC_* environment variables are placed between those two extremes in the priority order. (I regularly write LC_ALL=C to force all locale mechanics off in tests.)

Reference: POSIX, section 8.2 (Internationalization Variables): "The value of the LC_ALL environment variable has precedence over any of the other environment variables starting with LC_"

To understand the definition of these environment variables, read
http://www.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap08.html#tag_08_02