In addition to codes for individual languages and language groups, codes are also provided for three special situations.

Undetermined [und]:

This code is used if the language associated with an item cannot be determined.  This code is also used for works having textual content consisting of arbitrary syllables, humming or other human-produced sounds for which a language cannot be specified.

Multiple languages [mul]:

This code is used when two or more languages are associated with an item, and it is not practical to use codes for all of the languages.

No linguistic content [zxx]:

This code is used in place of a language code when the item has no sung, spoken, or written textual content (e.g., instrumental or electronic music; sound recordings consisting of nonverbal sounds; audiovisual materials with no narration, printed titles, or subtitles; machine-readable data files consisting of machine languages or character codes).

See also:

Introduction

MARC Code List for Languages:  Contents