This statement is true.  The French did not send their entire military to join in the fight, but they did formally take the side of the colonists after this battle.

Before the British surrendered at Saratoga, the French had been helping the colonists by providing them with weapons.  But Saratoga convinced them to go well beyond this.  After Saratoga, the French signed a formal pact with the US.  The French recognized the independence of the new nation.  They also pledged to give full military and financial support to the Americans.  This all came about because the Americans had proven the ability to defeat a true force of British regulars.