Finally we known date of new update 9.18. There was a news that the update will first be released on the North American server, as there are a lot of changes and the developers first want to run it on a smaller region than Russian (meaning the number of players in WOT).
Thus, the patch 9.18 for NA region will be released on April 18th.
The release date of update World of Tanks 0.9.18 on the Russian language cluster is on the night of April till 26th from April 27th.
Previously, all update originally came out for RU region and and only the next day updates was available for EU region. But this time the situation is a little bit mentioned. So as RU region is the biggest it will start only after testing on a smaller NA region. Release for Asia region will be 4th May