Localization/internationalization

[Gawdl3y]

The app should support multiple languages, especially given the diverse community that Resonite serves as home to.

Error messages from external crates on the backend are out-of-scope, as that would be nearly impossible to achieve with any consistency.

Error messages from Resolute's own code in the backend are doable since nearly all errors are already their own type and thus can be sent to the frontend via error codes rather than raw strings.