Including English, Reid has spoken about four languages throughout “Criminal Minds,” and according to some fans on Reddit, he understands far more. User real_mediageek noted that he had spoken Latin (likely due to his mother’s previous job as a professor in 15th-century literature) and Korean to assist in BAU cases. User fluffywhitething also mentioned his knowledge and affinity for the Russian language, which he admitted he was unable to speak or understand in Season 2 but is later seen watching a five-hour Russian film without subtitles in Season 6’s “Sense Memory.”
In Season 10’s “Rock Creek Park,” Reid also understands a woman speaking the African language Yoruba. According to other fans, the agent can also understand Spanish, and user Illyria_uk noted a moment in Season 11 where Reid also comprehends German. It is incredibly impressive that in the time we see Reid on “Criminal Minds,” he can understand seven different languages and speak four of them. It’s possible Reid taught himself these languages, given what we already know about his reading ability, intellect, and eidetic memory. Either way, he has served as an incredible asset to the team on multiple occasions, and we wouldn’t be surprised if he picked up new languages since the last time we saw him.