To obtain data on the status of history retranslation, use the command retranslator/get_stats:

svc=retranslator/get_stats&params={"itemId":<long>}

{
"au": <long>, /* the number of objects in the queue for retranslation */
"ru": <long>, /* the number of objects in the retranslator */
"hf": <long>, /* time 'from' */
"ht": <long>  /* time 'to' */
}