Steam route
Open the official Steam store listing for App 3393110, add the game to your library and install the release client. Players who used a separate test app should follow the official launch notice rather than assuming the test client becomes the live game.
PURPLE route
Use the download link from the official Global AION 2 website. Confirm that the website language and service region are Global before installing.
Avoid the wrong client
Korea and Taiwan packages are separate services. Avoid unofficial mirrors, torrent pages and look-alike download buttons.