The Battle.net app caches game data to load faster. If this cache becomes corrupted, the app gets stuck "preparing" data that doesn't exist.
Players have found several "workarounds" to bypass this frustrating loop: Match Language Settings : Ensure both the Battle.net App starcraft 2 preparing game data link
If you need to jump into a game immediately and want to bypass the looping Battle.net launch step, you can load the game client directly. The Battle
Ensure your in-game language settings match your Battle.net client settings. starcraft 2 preparing game data link
Locate the and Blizzard Entertainment folders and delete them.