Learn Farsi: دو کارآموز برای اضافه‌کار ماندن تلاش می‌کنن.

This sentence uses colloquial Tehrani pronunciation! In spoken Farsi, the 3rd-person plural ending -and drops the final -d and becomes just -an. So, the formal می‌کنند (they do) is spoken and written informally as می‌کنن.

Since there are "two" interns, why isn't the noun pluralized as کارآموزها?

In Farsi, whenever a noun is preceded by a specific number like دو (two), the noun itself must stay in the singular form. Even though کارآموز is grammatically singular here, the verb at the end of the sentence is plural (می‌کنن) because the subject is logically plural.

Why is the full infinitive ماندن (to stay) used in the middle of the sentence?

Here, the infinitive ماندن acts as a verbal noun, similar to the "-ing" form (gerund) in English. After the preposition برای (for), Farsi uses the infinitive to express the concept of the action. Literally, the phrase translates to "for overtime staying."

What is the structure of the verb تلاش می‌کنن at the end?

It is a compound verb built from تلاش (effort / struggle) and کردن (to do / to make). While English uses the single verb "try," Farsi uses this compound phrase, literally meaning "they make an effort."