Short background:
My first eyposure to Pratchett (which I didn't realize at the time) was when our German teacher picked the German version of "Only you can save Mankind" for us to read. It's very different from the average Discworld book but it was a great read and later realizing it was actually written by what would become possibly my favorite author makes it even better in retrospect.
It was about... five(?) years later that I bought another German translation of Pyramids and... I think it was Wyrd Sisters (because Pratchett was advertised as "the Douglas Adams of Fantasy" and I had just read the Hitchhiker stories not long ago) and after this bought a few German books kind of random-ish until starting to read the originals mostly in publication order.

That said... publication order is a nice thing, as long as you know the first few Pratchett is still developing. With books like "Guards! Guards!" you're pretty well served or Pyramids/Small Gods as standalones. Just don't start in the middle of a series, that would probably be a problem albeit not too much of one.

Also, while I love Discworld, why do people keep ignoring his other stories? Okay, Bromeliad, Strata, "Only you can..." can't really keep up with the Discworld but they are still good books and people mostly talk about them. Kind of a shame.