The target of this spell is unable to speak. Instead, balloons of ectoplasm materialise in the air above them. On the balloons are written the words they tried to utter, in the language they tried to use. The words will be spelled correctly, even if the 'speaker' is a poor speller or illiterate.
The balloons thus formed are lighter than air, and slowly float away. They dissolve after a few hours. They can be used as flotation devices, but they aren't sufficiently light to enable a human to fly. Crippled fairies have however been known to use a bunch tied together to stay airborne.
With particularly powerful examples of the spell strong feelings might cause ecoplasmic characters to appear; for example an exclamation mark for shock, a question mark for puzzlement, or a heart for love. In more powerful versions still, the character might find their thoughts materialised for all to read.