Code:
alias capitalize {
  var %x = $lower($1-)
  return $regsubex(%x,/^([a-zA-Zà-ú])|(\s[a-zA-Zà-ú])/g,$upper(\1))
}

alias cap.test { 
  echo -s teste -> $capitalize(test)
  echo -s café -> $capitalize(café)
  echo -s áries -> $capitalize(áries)
}


Result: