"用咝音发" can be translated into English as "pronounce with a sibilant sound" or "produce with a hissing sound", depending on the specific context and intended nuance.
"Sibilant" refers to a hissing or whistling sound, often produced when air is forced through a narrow opening in the mouth, such as in the pronunciation of sounds like /s/, /z/, /ʃ/ (sh), or /ʒ/ (zh in French).
"Hissing sound" is a more straightforward description, emphasizing the characteristic noise made by such sounds.
In a linguistic or phonetic context, "pronounce with a sibilant sound" would be the more precise and technical translation.