In Japan-occupied Korea, Koreans often mixed their spoken Japanese with Korean words like 아이고 ('gosh') and 나쁜 ('bad') and English words like 'slogan' and 'service' - in 1942, one Seoul police station cracked down on this by fining employees every time they uttered a Korean or English word

 

Gyeongseong Ilbo (Keijo Nippo), July 8, 1942

Saying "Aigo" also results in punishment

Seodaemun Police Officer Suggests a New Idea for Regular Use of Japanese Language

At the Seodaemun Police Station, Chief Yoshioka had been encouraging his staff to use the Japanese language in public and private life. On June 26, Detective Sergeant Hirayama came up with an ingenious idea and put it into practice as a model for others to follow, achieving very good results ahead of the other police stations in Seoul.

In short, it was decided that if anyone unintentionally used Korean or English while working in the station, even if it was just a word, they would be charged 10 sen each time.

Korean and Japanese employees used to exchange unpleasant words such as "aigo" and "nappeun" in Korean and "service" and "slogan" in English. But since then, these impure words have been cleanly eradicated as a result. The accumulated fines will be used as donations for the National Defense Fund.

Source: https://archive.org/details/kjnp-1942-07-08

Reddit Link: In Japan-occupied Korea, Koreans often mixed their spoken Japanese with Korean words like 아이고 ('gosh') and 나쁜 ('bad') and English words like 'slogan' and 'service' - in 1942, one Seoul police station cracked down on this by fining employees every time they uttered a Korean or English word : korea (reddit.com)

京城日報　昭和十七年七月八日

”アイゴー”も懲罰

国語常用に西大門署員が妙案

西大門署高等係では吉岡主任が予て同係職員たちに公私を問わず国語で通すよう慫慂していたが、平山部長刑事が去る二十六日妙案を考え出して実行。府内各署に先駆けて非常な好成績をあげて署内は素より各署職人に範を垂れた。

つまり署内で執務の際は仮令無意識にせよ朝鮮語若しくは英語等を使用した場合は、それが単語であっても一回につき金十銭也を徴収することを決議し実行している。

その結果、従来は内鮮職員が”アイゴー”とか”ナップン”とか英語では”サービス”とか”スローガン”等々の聞き憎い言葉が得々として交わされていたが、爾来これらの雑語類が綺麗に一掃された。積み立てた罰金はそっくり国防献金にするという。