[FEAT] Use selected language for greeting date and calendar

[acthelemann]

⚠️ IMPORTANT: Please fill out this template to give us as much information as possible to consider/implement the feature.

Prerequisites

• check this box if you have completed the following:
  • Reviewed the contributing guidelines and support files
  • Reviewed the README file for the repository you are working in
  • Searched for relevant instructions on our Discord server
  • Searched the issues of the repository you are working in to make sure one was not already filed

Summary

Use locale features in Date and react-calendar to translate into selected language.

• Greeting date uses selected language
• Calendar uses selected language

Motivation

We want everything translated that can be translated.

Possible Alternatives

Create a custom calendar with our own translations.

Additional Context

• new Date().toLocaleDateString('en')
• <Calendar locale="en">