ISO Language Codes
The ISO language codes are used for the "Language" and "Metadata Language" metadata fields in the Resource Metadata Exchange Agreement are derived from DublinCore dc:language. Both fields allows multiple values.
Please use the ISO 639 2-letter language codes whenever possible. Examples are “en, de, it, fr, et, es, sl, ro, bg”. See the first column in http://en.wikipedia.org/wiki/List_of_ISO_639-1_codes or http://www.ietf.org/rfc/rfc3066.txt. We currently do not expect to cover languages available only as three-letter codes.
It is desirable to distinguish language-neutral resources (like images without text on them) from those usable only under a specific language (images with text overlay, sound recording with a speaker announcing the organism, etc.). ISO 639-2 defines three code elements for special situations: mul (multiple languages) should be applied when many languages are used and it is not practical to specify all the appropriate language codes,und (undetermined) is provided for those situations in which a language or languages must be indicated but the language cannot be identified, and zxx (no linguistic content) may be applied in a situation in which a language identifier is required by system definition, but the item being described does not actually contain linguistic content.
We therefore request to code resources with unknown language as “und” (undetermined) and those that are language-neutral as “zxx” (“ind” is code for Indonesian!). Where necessary, metadata referring exclusively to scientific organism names may be coded more specifically as "zxx-x-taxon" (do not use the incorrect “la” for Latin).