Declaring 'html lang'

I have been chasing an accessibility error highlighted by the WAVE accessibility checker that says that the language is missing or not stated. Indeed the html line does not include a language declaration.

It appears that declaring the Site Language as English by default is not working, unless one first changes the language to something else and then back to English. Can this be fixed please?

@dan @tpbradley I have verified this bug myself. It would be great if you could look into this.

Thanks @MartWaring!

Thanks guys, this has been noted!

Cheers
Dan