Add commandline argument for different translations

[pjbull]

#108 added the Brazilian Portuguese translation of the checklist. We should add a few things to:

• Add a commandline argument that lets you specify a language code.
• Automatically generate a list of supported languages to appear in the documentation, readme, and commandline help based on the assets folder.
• Consider generating and linking to the translated version on the main deon webpage.

[pjbull]

We should bump up pri here when #124 gets merged so we can make both available.

[jayqi]

We might consider inferring a language from the OS-level locale setting and using that as the default if we support that language. https://docs.python.org/3/library/locale.html#locale.getdefaultlocale