Add multi-language support

[MarquisLP]

Is your feature request related to a problem? Please describe, and include issue number if applicable.

All of the app's UI text is hardcoded to English, which is of course an accessibility obstacle for non-English-speaking users of the app.

Describe the solution you'd like

The app should use an npm package like i18n to let the app dynamically load translated text based on the user's selected language.

We'll also need to add a new App Setting that allows the user to select a language.

One thing to consider is how we'll handle error messages. Right now, some error messages in the UI are taken from the error response we receive from world-scribe-2-server. We could either add localization to the server as well, or refactor things so that the error messages are only stored on the frontend. I'm leaning more toward the latter, as the former would add the extra overhead of needing to sync language selection between frontend and backend.

Describe alternatives you've considered

There may be other localization packages that are more suited to this project and/or are easier to integrate. Further research is required.