You select a target creature with the ability to speak within range & line of sight, they roll a Wisdom save against your spell save DC.

If they fail the WIS save, then for the spell's duration they will be unable to speak a language of your choice from their available languages, this will prevent them from communicating with their teammates, raising alarms, or casting spells with a Verbal component to them.

If they succeed on their WIS save, then they are only influenced by the above effect for a single round of combat.

For every 5 Character levels you have, you may choose an additional language to effect with this spell; at 13th Level this spell will effect all languages known by the target.

If, for any reason, this spell would target a creature who is unable to speak but may still comprehend a language, this will remove their ability to comprehend any languages. Additionally, if it targets a creature who cannot speak or comprehend languages, then it will instead deal 'x'd4 Force damage - with 'x' being the spell slot level it was cast at - to yourself & the target. That prior mentioned effect is due to the magical feedback caused by the spell being unable to work out how to work.