Learn Turkish: Mutlu yıllar! Yeni yıl başladı. - Happy new year! The new year has begun.

In Turkish, it is very common to use the plural form for greetings and well wishes. Mutlu yıllar literally translates to "Happy years." You will see this same pattern in other everyday greetings like iyi günler (good days) and iyi geceler (good nights).

Then why is it yeni yıl (singular) in the second sentence?

The second sentence is a normal statement of fact, not a greeting. Because it refers to the single, specific new year that just started, yıl remains in its singular form.

How is the word başladı built?

It comes from the verb başlamak, which means to begin or to start. By taking the verb root başla- and adding the past tense suffix -dı for "it", you get başladı (it started / it has begun).

Why does the English translation use "has begun" instead of "began"?

Turkish does not have a separate tense for "has done" (what English calls the present perfect tense). The Turkish simple past tense covers both "began" and "has begun" depending on what makes the most sense in context. For a new year that just started, "has begun" sounds more natural in English.