Learn Italian: Tradurre il dialetto è più facile di quello che sembra. - Translating the dialect is easier than it seems.

When comparing something to a full clause—meaning a phrase with a conjugated verb, like sembra (it seems)—you can't just use di or che. You have to use di quello che (literally "than that which") or di quanto.

Could we use di quanto here instead of di quello che?

Yes, you could say di quanto sembri. Notice that with di quanto, we normally use the subjunctive mood (sembri), which makes it sound slightly more formal. Di quello che is very common in everyday spoken Italian and comfortably pairs with the regular indicative mood (sembra).

Why is Tradurre (translating) in the infinitive form, and why doesn't it have an article?

In Italian, the infinitive form of a verb acts as the subject of a sentence, equivalent to the English "-ing" noun (gerund). It can stand entirely on its own without needing a definite article like il.

Could I use ciò che instead of quello che?

Absolutely. You can say di ciò che sembra. Both ciò che and quello che mean "that which" or "what." Quello che is just a bit more common in casual, conversational Italian.