Uma maneira é editar /etc/pam.d/login
da seguinte forma:
--- a/login 2015-06-15 03:35:17.422387358 +0200
+++ b/login 2015-06-15 03:36:41.535536201 +0200
@@ -50,7 +50,7 @@
session required pam_env.so readenv=1
# locale variables are also kept into /etc/default/locale in etch
# reading this file *in addition to /etc/environment* does not hurt
-session required pam_env.so readenv=1 envfile=/etc/default/locale
+session required pam_env.so readenv=1 user_readenv=1 envfile=/etc/default/locale
# Standard Un*x authentication.
@include common-auth
Não sei dizer se é o "jeito certo", no entanto.