Perhaps your iPad isn't capable of running Apple Intelligence.

From https://support.apple.com/en-gb/guide/ipad/ipade5045bb1/ipad...

"Apple Intelligence is available in iPadOS 18.1 or later on iPad models with M1 or later and iPad mini (A17 Pro)."

Your hardware needs to be fairly recent as well, for an iPad you need A17 Pro or M1 or newer. See [0] for the rest of the requirements.

[0] https://support.apple.com/en-us/121115

That probably means your iPad doesn’t support it. You need an iPad with an M series chip or the A17 Pro mini.

I had to change my system's language to "English (US)" for the privilege of running it.

There are a lot of reasons that it may not run at you, starting from from hardware or OS support, to being in the eu where eg iphone and ipad do not get it in eu right now but macs do for some reason.

https://support.apple.com/en-gb/121115

Apart from the HW requirements the others mentioned, Apple Intelligence is only available in the US (or at least it's not available in the EU). So make sure you're in the US.