The 27-year-old trained with Mick McCarthy's men for the first time on Monday and has been included in the squad for Tuesday night's Suffolk Premier Cup tie at Walsham Le Willows.
Youga started his career at French giants Lyon, where he trained alongside Real Madrid striker Karim Benzema and Chelsea's Florent Malouda.
He arrived at Charlton during the summer of 2005 and went on to make 71 appearances for the London club in his six years at The Valley.
Youga had loan spells at Bristol City, Bradford and Scunthorpe, but his progress at Charlton was hindered by knee problems.
The player joined Yeovil last January on a short term contract but left Huish Park by mutual consent in March.