Can I use a non-US keyboard to play GeForce NOW on SHIELD?

Yes. 

Follow these instructions to configure SHIELD for international keyboards

1. Install the latest SHIELD Experience Software Upgrade. 
   • Settings > About > Check for upgrades
2. Configure keyboards for correct language
   • Settings > Keyboards > Physical Keyboards
   • Set every device under Physical Keyboards to the same language
3. Verify in-game keyboard settings (key remapping may be required)