Can I use a 4-letter language code?

Hello,

I want to use en-GB language code on my website.

4-letter language codes are referenced in this Webflow support article: Glossary Term: Language code | Webflow Help

However I can only set a two-letter code in Webflow settings: Set your site's language code | Webflow University

Is this just a limitation of Webflow?

My site is https://www.venditan.com/

Thanks for any help.