Launcher says "update" but i have no internet

If the battle.net app has already recognized that the game client needs an update, then you would need to get and apply that update. There isn’t a direct way to cancel that update and make the game playable.

Depending on the size of the update, and if you have the capability you can try using a cellular hotspot to nab the update (You will need a wireless connection and a hotspot data plan for your mobile device and those plans are usually limited in the amount of data you can use each month) or maybe take the system (if portable) to a public wifi or a friend/family member’s place to snag the update.