Small spec change required by RFC for lang params

[colecmac at protonmail.com]

I found another small error in this section, might as well put it here.

It says:

> Valid values for the "lang" parameter are comma-separated lists of one
> or more language tags as defined in RFC4646.

But RFC4646[1] is obsoleted by RFC5646, which is more commonly known as
BCP47[2]. The spec should be updated to reflect this, saying:

> Valid values for the "lang" parameter are comma-separated lists of one
> or more language tags as defined in BCP47.

It would be nice if it linked to BCP47 as well.

1: https://tools.ietf.org/html/rfc4646
2: https://tools.ietf.org/html/bcp47


Thanks,
makeworld