[rilmodem] Set current UI system language to environment variable

Read current terminal UI language from configuration file and set it as
environment variable for provide local information proactive command.

Signed-off-by: Petri Takalokastari <petri.takalokastari@oss.tieto.com>
Merge pull request #176 from ptakalok/language

[rilmodem] Set current UI system language to environment variable