OK, I restored the internet sharing. If you leave Spanish keyboard installed on device before the upgrade, YOU WILL LOSE the ability to share internet after Lumia Black update.
To enable internet sharing / tethering -
First option (If you have not upgraded to Lumia Black yet) -
1. Remove all non-english keyboards from device before installing the Lumia Black update. (Settings--> Keyboard)
2. After the Lumia Black upgrade finishes, install Spanish (Mexico or Spain) keyboards. (Settings--> Keyboard--> Add keyboard)
Second option (if you have already installed Lumia Black firmware) -
1. BACKUP ALL CONTENTS OF YOUR PHONE (you will likely lose everything)
1. Remove/delete all non-english keyboards from device. (Settings--> Keyboard)
2. Reset the device (Settings--> About --> Reset your phone). CAREFUL - YOU WILL LOSE ALL DATA ON PHONE!
3. After reset is complete, install Spanish (Mexico or Spain) keyboards. (Settings--> Keyboard--> Add keyboard)