The Tree of Savior team has posted a brief notice that regional cross server party matching has been hotfixed into the game. The fix was patched in to reduce wait times in both North American and SEA regions in particular.
We have added a hotfix that will allow cross server automatic party matching between the servers within the same region.
For example, a player from the Klaipeda server will be able to play with a player from the Orsha server via the automatic party matching system as they are both from the NA region.
Source: Tree of Savior official site