Sworn translation and notarisation are two steps

Why a good translation can still be rejected

Accuracy is not the test. A fluent translation done by a bilingual friend has no standing, because the system is authenticating a registered person rather than judging the language. The translator's registration is the point.

Apostilles are a third thing

Documents issued abroad often need an apostille from the issuing country before Turkey will look at them. That is obtained at home, before you travel, and it is the step most likely to send somebody back across a border.

Birth and marriage certificates are the usual candidates. Ask early, because the process at home can take longer than everything in Turkey combined.

Keeping the cost sane

Translate only what is asked for. The document list is specific, and translating a folder of extras is a common and avoidable expense. Where a service quotes translations inside a package, ask how many documents that covers and what happens if the office asks for one more.