From Hull AWE
Radicchio, a form of chicory, used in salads like lettuce, is pronounced as it is written - but in different languages, the rules are different, producing different results.
- In English, where the '-h-' as a rule makes the '-c-' soft, radicchio is often pronounced 'rad-EACH (or ITCH)-i-oh' (IPA: /rad ˈiː (or ɪ)tʃ ɪ o/), although both OED and LPD prefer it in the Italian sound below. The plural recommended by ODE is radicchios.
- In Italian, which has given the word to English, the '-h-' has the opposite effect: it makes the '-c-' hard. The Italian pronunciation is 'rad-IKK-i-oh' (IPA: /rad ˈiː ki o/). (The Italian plural is radicchi, 'rad-eek-e', /rad ˈiː kiː/.)
AWE recommends that you use the Italian pronunciation and the English plural. (This is different from the recommendation for pistachio.)