The Korean-language drama is about an alternative world where people in debt compete in deadly games.
But fluent Korean speaker Youngmi Mayer claims the closed-caption subtitles in English are "so bad" that the original meaning is often lost, reports the BBC.
Netflix hasn't yet responded to Newsbeat's request for comment.
The series has proved hugely popular since its release last month and is on track to beat Bridgerton to become Netflix's biggest original series.
The plot sees a group of people tempted into a survival game where they have the chance to walk away with 45.6 billion Korean won (£29m) if they win a series of six games.
If they lose, they die.
'Character's purpose lost'
"The dialogue was so well written and zero of it was preserved [in the subtitles]," Youngmi said in a Twitter post.
In a TikTok video that's had almost nine million views, Youngmi gave several examples of mistranslation.
In one scene a character tries to convince people to play the game with her, and the closed-caption subtitles read: "I'm not a genius, but I still got it worked out."
But what the character actually says, Youngmi explains, is: "I am very smart, I just never got a chance to study."
That translation puts more emphasis on the wealth disparity in society - which is also a theme in the Oscar-winning 2019 Korean film, Parasite.
"Almost everything she says is being botched translation-wise… the writers, all they want you to know about her is that," Youngmi said.
"[It] seems so small, but it's the entire character's purpose of being in the show."
Fans commenting on Youngmi's thread have questioned Netflix's translation strategy, and others have pointed out that less accurate captions make it difficult for those trying to learn a new language.
Youngmi's initial comments were about the closed-caption subtitles rather than the English language subtitles.
Closed captions are for people who are hard of hearing and include audio descriptions and sound effects, as well as speech. They're often automatically generated.
Youngmi has since clarified that the English language subtitles are "substantially better" than the closed-caption ones.
But she added: "The misses in the metaphors - and what the writers were trying to actually say - are still pretty present."
Newsbeat has asked Netflix to respond to the claims.