Retired in ISO 639-3: Merge with Halh Mongolian [khk]
Excerpt from change request document:
Darkhat is in reality a dialect or regional accent variation of Mongolian Halh (Darkhad or Darhad is often used for transcription of its standard form in Halh; Darkhat is the preferred older, traditional orthography.) When Darkhad speakers converse with Halh speakers from other regions they understand each other fully without difficulty. They consider their language to be Halh.