Please add the language code sth to the list of language codes supported for monolingual text values.

Usage example: Shelta is a mixed language spoken by the Rilantu Mincéirí indigenous to Ireland. It is a mix between Irish and Hiberno-English. I think it would be useful to add it so this language can be preserved. One of the places where it would be especially useful is on Q36705 and Q875651 and on other Rilantu Mincéirí and Shelta related wikidatas