Around 400 to 500 people apply to join the force annually but only around 12 percent of applicants are selected for training in the police academy, cantonal police spokesman Marco Cortsei told media.
The first stumbling block for candidates is that they have to be Swiss citizens.
The next hurdle is passing a German aptitude test, which most (51 percent) candidates fail, the Tages Anzeiger newspaper reported on Wednesday.
The test includes grammar, dictation and an oral examination.
“There have always been German problems with candidates,” Cortesi told Tages Anzeiger.
“But these are on the rise.”
Many candidates stumble when it comes to describing situations correctly in faultless German while dictation is the “biggest cliff”, Cortesi said.
Most candidates have been out of school for several years so their German skills are “a little rusty”, Werner Schaub, media relations chief for Zurich police is quoted as saying.
City and cantonal police recommended that candidates urgently refresh their knowledge of German before taking an entrance test.
A police officer's job involves a lot of paperwork with extensive reporting required, officials underlined.
Solid German skills are fundamental because police reports go to investigating authorities and the courts, Cortesi told Tages Anzeiger.
“Poorly written or orthographically incorrect reports are picked apart by lawyers.”
German, one of Switzerland's three official languages (the other two being French and Italian), is the primary language in the canton of Zurich, where it is spoken with a regional dialect.
Instructors of German point to the rise of social media and smartphone messaging, which is giving rise to the use of slang and abbreviations.
“As a result many lose the exposure to correct German,” German teacher Markus Senn told Tages Anzeiger.
The daily said the situation has given rise to the joke that the worst enemy of police in Zurich is not criminals — but the German language.