What metadata schemes are there for the description of linguistic resources?

Quite a few. Examples are: Dublin Core,

Open Language Archives Community

See: http://www.language-archives.org

(which is an enriched version of Dublin Core),

ISLE Meta Data Initiative

See: http://en.wikipedia.org/wiki/IMDI

, the

Text Encoding Initiative

See: http://en.wikipedia.org/wiki/Text_Encoding_Initiative

header.