This category is triggered by language infoboxes which do not contain any language codes, such as ISO 639-3, LingList, Guthrie, etc. (ISO 639-2 does not count, as it is not language-specific in such cases.)
Ideally, this category should be empty, apart from unclassified varieties such as Danzhou dialect, which (as of 2012) are not clearly a dialect of an ISO language, but not clearly a distinct language either.
For languages which are simply not covered by ISO, enter
iso3=none, and the article will appear in a dedicated category.
For dialects of languages which are covered by ISO, add the parameter
isoexception=dialect. This is how dialects should normally be treated, as ISO codes are not generally dialect-specific and therefore should not be used in such cases;
iso3=none is similarly inappropriate for dialects subsumed under the ISO code of their parent language. Linguist List, Linguasphere, Guthrie and AIATSIS may, however, provide dedicated codes that are appropriate for dialect articles; if one of these is added, the article will appear in a separate category.
isoexception is set to
talkpage, the article won't be listed in any category at all. This is used so that archived talk pages with discussions of the info box won't pollute the category.