Add commandline argument for different translations

#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.

Start by inspecting the assets folder and the existing command-line entry point, then review the documentation, README, command-line help, and main deon webpage. Define how supported languages are discovered and exposed before implementing the language-code argument and generated links. Done means translations are selectable and the supported-language information is consistent across the listed surfaces.

Written by the indexing model from the issue text.