"无人委托诉讼的" can be translated as "where there is no one to entrust with the litigation" or more naturally in legal contexts, "where no one has been entrusted to conduct the litigation".
Here’s a more contextually appropriate example sentence:
"In cases where no one has been entrusted to conduct the litigation, the court may take appropriate measures in accordance with the law." (无人委托诉讼的,法院可以依法采取相应措施。)