Learn Turkish: Kütüphaneci çalışıyorken sessiz olunur. - One is quiet while the librarian is working.

olunur is the passive form of olmak (to be). In Turkish, adding the passive suffix to an intransitive verb (a verb without a direct object) creates an "impersonal" meaning, like "one does" or "people do". Combined with the aorist tense suffix -ur, it states a general rule: "one is quiet".

Why does the passive suffix for olmak use -un instead of -ıl?

Normally, verb roots ending in a consonant take -ıl or -il to become passive. However, if the root ends in the letter L, it takes -ın, -in, -un, or -ün instead to avoid repeating the L sound. Therefore, ol becomes olunmak.

What is the difference between using çalışıyorken and çalışırken here?

The suffix -(y)ken ("while") can attach to different verb tenses. çalışırken uses the aorist tense and means "while working" as a general, everyday fact. çalışıyorken uses the present continuous (-ıyor) and emphasizes being right in the middle of the action. Both work perfectly here, but çalışıyorken paints a more vivid picture of the ongoing work.

Is kütüphaneci the subject of the entire sentence?