here's a JS one liner that handles scream and unscream in one function

  transform=s=>[...s.toUpperCase()].map(s=>(l="BÁGẲLẬQǞVÀCĂHẴMẦRȦWẢDẮIǍNẨSǠXȂEẶJÂOẪTẠYĀFẰKẤPÄUȀZĄ")[l.indexOf(s)^1]||s).join``