Julia Roberts is in The City of Light ... and, her smile can light up a room -- 'cause she was grinning wide while walking into the César Awards in Paris!

The famed actress stepped out Friday for the ceremony wearing a chic black ensemble ... and, she looked to be enjoying her European vacay.

Roberts flashed her grin for photogs on her way into the building ... before she went inside to accept her Honorary César -- a lifetime achievement award from the Académie des Arts et Techniques du Cinéma.

Julia received a long standing ovation from the crowd while accepting the honor ... before giving a speech without the aid of notecards -- and struggling to put into words what it meant to her.

The César Awards are essentially the Oscars put on by the Parisian-based group. ... and, they handed out a ton of awards last night -- including Best Film to the controversial flick Emilia Perez which has been nominated for 13 Oscars.

The films nominated are all non-English movies it seems ... so, flicks like "Wicked" and actors like Timothée Chalamet weren't up for anything at the ceremony.

The Oscars are tomorrow ... and, it looks like Julia might be skipping the biggest night in Hollywood to enjoy the Champs-Élysées and the Seine.

Can't fault her for that!