Forced arbitration and picking jurisdictions is illegal in the EU so that clause doesn’t apply to Austria. An Austrian would file in any Austrian court that has jurisdiction for contract/civil matter. Therefore, the section with King County includes:

For All Subscribers Outside the European Union and United Kingdom: […] You and Valve agree that all disputes and claims between you and Valve (including any dispute or claim that arose before the existence of this or any prior agreement) shall be commenced and maintained exclusively in any state or federal court located in King County, Washington, having subject matter jurisdiction.