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

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)