The obverse bears bust of Franklin, left. Around, BENJ. FRANKLIN NATUS BOSTON. XVII JAN. / MDCCVI; signed on truncation, DUPRE. F
The reverse bears nude winged genius, broken crown and scepter at his feet, lightning striking towards rotunda at left. Around, ERIPUIT COELO FULMEN - SCEPTRUM QUE TYRANNIS; in exergue, SCULPSIT ET DICAVIT / AUG. DUPRE ANNO / MDCCLXXXIV
The latin legend around the reverse can be translated to "He seized lightning from the heavens and the scepter from tyrants." The legend in the exergue translates to "Engraved and dedicated by Augustin Dupré in the year 1784"
Franklin had been sent to Paris in 1776 to negotiate an alliance with France and had quickly become a hugely popular figure. Adams and Bentley conclude that this medal was sponsored by a private friend (or group of friends) to honor him.
A second medal, also engraved by Dupré, was issued two years later. Both medals share the same obverse die and the same reverse inscription, but where the earlier medal features the winged genius on the reverse, the later one merely features an oak wreath. That later version was sponsored by Louis XVI.
As with many of the early American medals that were originally struck in France, there are numerous later restrikes. I do not yet have the expertise to distinguish an early original from a later restrike. Maybe someone with the requisite experience can help out. If I'm correct, this medal is usually referred to as Betts-619.