In this episode, Data has a brief conversation in French with a gentleman playing poker in Ten Forward. However, there's no actual dialogue provided in the episode. Data merely mentions that he can understand and speak French, and the gentleman comments on how well Data speaks it.
The scene is meant to highlight Data's ability to learn and assimilate human customs, including languages, even though he doesn't fully understand the social nuances of the interaction.
It's important to note that, although this is a popular fan interpretation, there's no record of the actual French phrases used in the episode.