Use actual compiled language for lang command

Summary:
While addressing T1131 and removing the command lang from Nasqueron production
branch (see D3199), it was noticed this function always return English whatver
the language selected at compile time.

This change allows this command to be useful and output the actual language.

Test Plan:

13:24:25 -!- Odderon0 [dereckson@nasqueron/bot/Odderon] has joined #pentacle
13:24:29 < DcK> Odderon0: lang
13:24:29 < Odderon0> DcK: I speak French.

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D3200