Configurable Locale for Email Previews

[NikoHadouken]

Currently, when developing emails using yarn dev:emails, the en locale is hard-coded in the previewEmailContext. It would be helpful to have a way to specify a different locale for email previews, allowing developers to test localized content more easily.

[NikoHadouken]

Hi @lukevella,

I already did some research and found a fix how to use a different locale in the react-email previews.
We could use an env var like the existing REACT_EMAIL_LANG to pass the locale when developing emails like REACT_EMAIL_LANG=de yarn dev:emails.

If you like, you could transfer this into an issue and I would submit a PR for this so you can take a look.