Look into using standard tooling for translations

[goodmami]

The MultiString class for managing translations of the documentation was intended for use with a templating system like Jinja2. This works fine for now (although we haven't made much use of it yet), but we may want to eventually consider a more standard tool for this, such as the gettext module in the standard library. Maybe we could wrap gettext's class-based API with something to maintain a similar usage to MultiString.