The ISO 639-3 language codes in the range qaa–qtz are 'reserved for local use'. Any organization or person may use them to designate whatever languages they want, as long as they are not mistaken for code assignments in the standard. It is not known in general who is using them for what purposes, as such use may be private.

One organization, however, the Linguist List, makes its assignments known publicly, using them primarily to refer to extinct languages (a class of languages that are often missing from the standard). The Linguist List's codes are not official ISO 639-3 codes, but are compatible with the official standard, and may be safely used as long as their identity as local codes assigned by the Linguist List is made clear and they are not confused with local language codes assigned by other parties.

Following are the values Linguist List has assigned to this range, as of 2013 Sep 01. Names are those listed at the top of the Linguist List entry; additional names in the body of the entry are not repeated here. The Linguist List entry can be seen by following the link at the beginning of each line.

There is no requirement that a language name be identified before it is assigned a code in the private-use range. As a result, a large number of these code assignments are redundant, some even assigned to the appearance of a language in a specific source. Many of the languages have official ISO codes, though not always on a one-to-one basis with the local codes.

• Ypsilanti, MI (2009), Multitree: A digital library of language relationships, Institute for Language Information and Technology (LINGUIST List), Eastern Michigan University