Fianchetto is commonly pronounced in English as /fiænˈtʃɛtoʊ/ (soft ch as in "cherry") but the original Italian word is pronounced /fjaŋˈketto/ (hard ch as in "chaos"). Note the word is cognate to English flank.
It is common for terms borrowed from other languages to take on 'erroneous' pronunciations if the inherited orthography is ambiguous e.g.
- cherub (Latin: /k/; English /tʃ/)
- pistachio (Italian: /k/; English /tʃ/)
- bruschetta (Italian: /sk/; English: /ʃ/)