Thank you for using Apple Support Communities. It's my understanding that the Spanish Siri voice doesn't work on your iPhone. I'm happy to help.
If you haven't already, restart your iPhone. Restarting can resolve many unexpected behaviors.
Restart your iPhone, iPad, and iPod touch
If the issue persists, reinstall iOS with iTunes. This can resolve possible software issues. When reinstalling iOS, iTunes will completely remove your current software and install a fresh version. While iTunes will try to do this without removing data, it's a good idea to make sure you have a recent backup before trying this step.
How to back up your iPhone, iPad, and iPod touch
Use the steps in the link below to reinstall iOS with iTunes:
If you can't update or restore your iPhone, iPad, or iPod touch
Please let us know if the issue continues and include any other troubleshooting steps you may have tried.
Have a great day!