I'm pretty sure that unicode characters are not legal for HTTP field values, as RFC7230 says:
Historically, HTTP has allowed field content with text in the
ISO-8859-1 charset [ISO-8859-1], supporting other charsets only
through use of [RFC2047] encoding. In practice, most HTTP header
field values use only a subset of the US-ASCII charset [USASCII].
Newly defined header fields SHOULD limit their field values to
US-ASCII octets. A recipient SHOULD treat other octets in field
content (obs-text) as opaque data.
So I don't think that header is legal... but it should not fail in hpack, whose RFC says it should treat fields as opaque octets!
Thus I think the generation of the header is wrong, but also the way that jetty fails is wrong.