Rahul referred to an interview Modi gave at the Nanyang Technological University (NTU) in Singapore during his recent visit.
After Modi answered a question in Hindi, the interpreter started reading from a piece of paper, prompting speculation that the script may be "pre-planned".
"The first Indian PM who takes 'spontaneous' questions that the translator has pre-scripted answers to!
"Good that he doesn't take real questions. Would have been a real embarrassment to us all if he did," Gandhi said on Twitter.
He also tagged a video of Modi's question where the translator is heard purportedly reading out a scripted answer.
Gandhi is currently abroad along with his mother and UPA chairperson Sonia Gandhi who had gone for a medical check-up to the United States.
On Sunday, Congress leader Shashi Tharoor had tweeted while tagging a news report on the NTU interview, "Oh dear. When the translator says what the PM was supposed to say, but didn't".
(With PTI inputs)