ID for language-invariant strings

Doug Ewell doug at
Tue Mar 18 16:02:11 CET 2008

Mark Davis <mark dot davis at icu dash project dot org> wrote:

> "und" means "undetermined". Not "cannot figure out what language this 
> stuff is in", not "cannot be determined", just "undetermined". That is 
> about as neutral as you can be.

Much has been made of the fact that ISO 639-3, unlike -1 and -2, 
provides pointers to specific descriptions of what the code elements 
mean.  Here is the description of "special" code elements from the 
official ISO 639-3 site (

Special situations

ISO 639-2 defines three code elements for other special situations. The 
identifier [mul] (multiple languages) should be applied when many 
languages are used and it is not practical to specify all the 
appropriate language codes. The identifier [und] (undetermined) is 
provided for those situations in which a language or languages must be 
indicated but the language cannot be identified. The identifier [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.

The relevant passage for our purposes is "the language cannot be 

Doug Ewell  *  Fullerton, California, USA  *  RFC 4645  *  UTN #14  ˆ

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