There is no Wiktionary test project for Belarusian (Taraškievica orthography). Please consult Wiktionary in Belarusian for further information.
be-tarask is not a valid ISO 639 code in and of itself. It uses an IETF language tag (BCP 47 extension) instead. Use of this code has been previously approved by the Language Committee, and a Wikipedia exists under the code.