Appointments: make user-specified description translatable

[WilliamDEdwards]

Is your feature request related to a problem? Please describe.

When creating an appointment, the user can specify a 'description'.

However, the 'book appointment' page is not necessarily in the same language, causing the mixing of languages.

Describe the solution you'd like

This issue would be solved when the user can translate the description for specific locales, and default to one, such as English (because users won't translate their descriptions to all languages that NextCloud supports).

Describe alternatives you've considered

Simply accept that the 'book appointment' page contains multiple languages, but it's ugly / unpolished.

Additional context

From a technical standpoint, implementing a translation system seems overly complex. But I don't see any alternative other than tolerating the mixing of languages.