How to unhide a Bluetooth device?

Please explain what you mean. You can't "hide" a bluetooth device. You can delete one, in which case, if you want to use your phone with it again, you will need to re-pair it with the device. Settings>General>Bluetooth. See the documentation for the device you wish to pair with for instructions to set it into discoverable mode.

I don't have anything that equates to "Hide" when I look at the bluetooth screen for a device on my phone in English.

The top option on the page is "Forget this Device". That sill effectively delete the pairing.

I think you need to re-pair your phone with whatever you're trying to connect to.