Include user's desired language code

It looks like the user language is not reported:

I'm not familiar with the GA4 protocol. But the info is in the Accept-Language request header.

As example, my browser's language header is pretty long:

Accept-Language: en-DE,en-US;q=0.9,en;q=0.8,de-DE;q=0.7,de;q=0.6,en-GB;q=0.5

I'd expect that to register as simply "English" but probably GA wants the most preferred language code so en-DE.

I put /x/ga in front of a blog in a multilingual region so it's good to know what the expected user languages are.