Hard-coded REGLANG_NOTIFY_USER is causing problems.

REGLANG_NOTIFY_USER is declared as a constant in reglang.module.

On line 114 the following condition is checked:

if (REGLANG_NOTIFY_USER) {

Since REGLANG_NOTIFY_USER has been defined as a constant and there is no other place where it is referred to in the code then this condition is dependent on the value of REGLANG_NOTIFY_USER as hardcoded into this file (as a constant). It is hard-coded to be true so the following variable is set to be an empty value when the user is registering:

//current user
        $message['language'] = user_preferred_language($message['params']['account']);