They are all palatal sibilants in Japanese, while in English they’re palato-alveolar. And the “ch”/“j”/“sh”/“zh” sounds I speak of are just common variations of “t”/“d”/“s”/“z” that occur before “i” (they are spelled si -> shi, zi -> zhi, ti -> chi, di -> ji). Usually “zhi” isn’t spelled out in Rōmaji though. The “h” in “hi” also sounds different. Before “u” some consonants also change (hu -> fu, tu -> tsu, du -> dzu).
These sound changes don’t occur for all speakers/dialects, some don’t have a “shi” and just say “si” for example, but they are the most common and standard I believe.
Wait, how does ch/j or sh differ from the English sounds? And what words use zh? I don’t think I’ve seen that romaji
They are all palatal sibilants in Japanese, while in English they’re palato-alveolar. And the “ch”/“j”/“sh”/“zh” sounds I speak of are just common variations of “t”/“d”/“s”/“z” that occur before “i” (they are spelled si -> shi, zi -> zhi, ti -> chi, di -> ji). Usually “zhi” isn’t spelled out in Rōmaji though. The “h” in “hi” also sounds different. Before “u” some consonants also change (hu -> fu, tu -> tsu, du -> dzu).
These sound changes don’t occur for all speakers/dialects, some don’t have a “shi” and just say “si” for example, but they are the most common and standard I believe.