If you play BDO on steam and your location is in SEA but after you download bdo from steam and the client is TR/Turkey server instead of SEA don't sing up yet, don't patch it yet and don't uninstall yet, Instead of reinstall it from steam you just need to download SEA server client from https://www.sea.playblackdesert.com/Data/Down/  after that, just copy paste all the files from SEA client directory to your "BlackDesert" folder on C:\Program Files (x86)\Steam\steamapps\common . It will change from TR/Turkey language and server into SEA. 

i face this issues twice and manage to change it again from TR/Turkey to SEA. hope it works for you Good Luck..

Thanks you it's work for me

if i used to have an account on bdo sea steam will the account come back? because I can't login to the bdo account from steam until now

Great it worked. You can copy after the official client (Data/Down) patched full. Then paste to steam.
I am not sure whether when you copy, you better exit steam or not
When you start the game, it will have long recheck. (If nothing go wrong it should able to press play) Else it redownload thailand, then you know your screw up. Copy again maybe.

Thank you so much

If bdo has an update, will steam download the data of the turkey server or will it still download the data of the sea server?

nope, this happened to me, it used turkey region again

well, when you update, you need to reinstall it back and redo it again

Hi guys I have the same problem, whenever there is an update even just a small patch, steam will redownload entire game, then it goes back to turkey server again, then I had to do again the process of downloading the client from https://www.sea.playblackdesert.com/Data/Down/ paste it again in steam common folder repeating this process, that @MadDogChan suggested. Though it works It is quite a hastle because it is a large file that needs to be redownloaded twice. If you guys have another solution for preferably faster please post it here thanks. It seems that steam and pearly abyss haven't found a fix for this issue yet and if there is please give me the link. By the way on my friend's account where I bought him BDO as a gift, he is not encountering this problem.

Yeah same problem. Due to lack of space, i only copied SEA paks files, and replace it whenever there is an update. If you have enough storage space, just copy PAKS files from TK and SEA and replace accordingly during updates. I am currently attempting to contact PA support and Steam Support to see if there is any fixs for this. PA is no help like usual and Steam says it might be due to the complimentary version of BDO. Will update if my problem got fixed. You only need to do the process of replacing the client files once. After you able to play in SEA version, copy the service.ini and config.ini and keep it in a save location. Replace only that both & SEA paks whenever there is a need to change to SEA client.