Aphasia

You attempt to befuddle a creature such that it can no longer put its thoughts into comprehensible expression.

Choose a creature within range.  The target must succeed on an Intelligence saving throw or be affected by the spell for duration.  If the creature you choose has an Intelligence of 3 or lower or doesn't speak any language, the creature is unaffected.  An affected creature loses the ability to communicate with other creatures in any way and to cast spells with vocal components.  When an attempt is made, the affected creature's communication does not come across as sensible in any way to the recipient, i.e. the creature may use completely different words or gestures than it means to.  The affected creature's thoughts are unaffected and a spell such as detect thoughts will reveal what the creature is intending to to communicate.

A creature is affected for the duration or until dispelled by dispel magic or similar effect.

At Higher Levels. The duration of the spell increases to 1 hour when cast at 4th or 5th level, 8 hours at 6th or 7th level, and until dispelled at 8th or 9th level.