No locale support

[ivar-it]

Hello and thanks for this good dockerization of sopel =)

It seems there is no support for locales in this.
Would it possible to add?

Some modules im using are crashing because of trying to use locale.
ValueError: Currency formatting is not possible using the 'C' locale. (file "/usr/local/lib/python3.6/locale.py", line 262, in currency)

Many thanks in advance and have a nice day!