It's against the law in North Korea to use South Korean words

 From Radio Free Asia:

North Korea sentences 20 young athletes for ‘speaking like South Koreans’. Skaters and skiers were caught on video using banned words while playing a game during training.  By Jieun Kim for RFA Korean

"About 20 aspiring North Korean winter athletes were abruptly sentenced to three to five years of hard labor in prison camps after they were found to have used South Korean vocabulary and slang while playing a word game, sources in the country say.

"It’s the latest example of authorities imposing draconian punishments to try to stamp out use of the “puppet language” and “capitalist” influences in daily life – despite the flood of illegal South Korean dramas and songs that many North Koreans secretly watch after obtaining them on thumb drives smuggled into the country.

"The ice skaters and skiers, all high school graduates under the age of 25 from Ryanggang province, were publicly disgraced at a square in Hyesan on April 3, a resident in the city on the Chinese border told Radio Free Asia’s Korean Service on condition of anonymity for security reasons.

“Residents think that it is excessive that they were sentenced between three and five years” of hard labor, another source in the city said. “It would be impossible to count how many hundreds or thousands of South Korean movies and dramas are easily available to us.”

...

"Apparently, one of the athletes took a video of the young people playing a word game called mal kkori itgi, where the object is to make a sentence that starts with the final word of the previous player’s sentence, and some of the athletes used vocabulary that was distinctly South Korean, a second source from the same province said.

"The video was found on the phone of one of the female athletes during a random inspection raid by police of her home – a frequent occurrence in North Korea when police look for contraband – and was reported to authorities. It wasn’t clear if she had taken the video or if it was sent to her, the first source said.

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"The North Korean government recently passed the Pyongyang Cultural Language Protection Act, which underscores that the Pyongyang dialect is the standard language, and doles out severe punishments for speaking like a South Korean, or the death penalty for teaching others how to."