The agreement is that the fight will take place in Mexico, though the specific venue is yet to be agreed, and it will take place on May 10th.
A week or so ago it seemed likely that Onesongchai were going to try and force purse bids though from what we understand they were happy to take a larger payment to allow the fight to take place in Mexico. Effectively letting their man get the best deal possible in terms of finances.
Other details that seem to have emerged is that Thai television will pick the fight up live, a worry originally considering the time difference. In Japan we would expect the bout to be shown on TBS, though it may be on tape delay.
(Image, of Pungluang, courtesy of Onesongchai)