From the Super Mario Wiki
The Yoshi Theater is a theater located north of Beanbean Castle Town in Mario & Luigi: Superstar Saga, and was built specially to honor the Yoshis. Boddle, Bubbles's brother is the curator. After the Mario brothers obtain the seven Neon Eggs, Boddle places them on the sign and the Yoshi Theater opens while the Yoshis celebrate.
The Yoshi Theater is the only place to see Yoshis in the game, not counting the ending.
 Movies Showing In the Yoshi Theater
All of the movies showing at the Yoshi Theater are based on games within the Nintendo universe (including Mario & Luigi itself).
 Names in Other Languages