Add translations for contact-facing pages

[driaug]

Hey all!

If you want to contribute to Plunk in an easy way you can now do so!
You can help by adding translations for our contact-facing pages and unsubscribe footers.

How to add a translation

1. Create a new .json file in packages/shared/src/i18n/locales with the ISO 639-1 code of your translation
2. Add your language to the SUPPORTED_LANGUAGES in packages/shared/src/i18n/languages.ts
3. Import and add your translations to packages/shared/src/i18n/index.ts
4. Add the translations in your newly created .json file