Ukraine dictating sentencing rules in a U.S. criminal case, is not unlike Nanzi Pelosi dictating Senate procedures in the impeachment hearing.
Pretty much a non factor.
In case of another US Army defector and a Right Sector Nazi traitor Alex Zwiefelhofer who was Lang’s accomplice it might be the case. Lang is still under Ukrainian jurisdiction. They might try him themselves, sentence to suspended term and bring back to his Nazi unit.