There is a “code” for language (English, Spanish, etc…) not defined?

Question

In my application there is language detection. Languages have some identification code like en for English, pt for Portuguese, fr for French, etc.

Is there a language code for the case when a language cannot be identified (unknown language)?

Answer 1

The language codes you're using look like ISO 639-1. There is no ISO 639-1 code for an indeterminate or unknown language; however, "xx" could be used as as a reasonable placeholder.

Answer 2

If your system allows for three-letter codes, the ISO 639-2 standard says:

If there is language content, but the specific language cannot be determined, a special identifier is provided by ISO 639-2:

und (Undetermined)

Answer 3

You probably know it already, but at least for the benefit of others who may look your question up later:

In C, C++ and Unix/Linux generally, and sometimes elsewhere, there is something that goes by the cryptic name of "the C locale." This is really the absence of a locale, which is to say, the absence of a set of language- and country-related conventions. In the C locale, text is sorted in straight character-code (usually ASCII) order, which means that "ABC" precedes "XYZ" precedes "abc" precedes "xyz."

One needn't specify any code at all to get the C locale. It has no code -- a significant fact which is at least tangentially related to your question.