According to their post, the Dota 2 world championship will be held on August 16-25. Matches of the group stage will be carried out in the first three days and the playoff stage will be hosted on August 20-25.
With regard to the organizer of the tournament, Valve hasn't responded to the statement. It's worth to remind that last year, the events of The International 2018 happened on August 15-25 and this means that the information might be pretty truthful.
At the moment, only four participants are known, which have earned a big number of Dota Pro Circuit points and will go to TI2019: Virtus.pro, Team Secret, Vici Gaming, and Evil Geniuses. This year, The International will take place in Shanghai, China and Mercedes-Benz Arena will be a venue.