"Spring is very beautiful."
Translation:İlkbahar çok güzel.
turks have ilkbahar which means first and sonbahar is fall.sonbahar is the second bahar or last bahar. Son+bahar, is son here means second or last?
It's correct but it's not literally the translation of the English sentence.
Why is it: Ocak bir ayDIR, and why not: Ilkbahar çok güzelDIR? When with "to be" are you using nothing and when - dir etc? Is it optional?
Yes it is optional. Generally we use it in general statements.
ps. The correct sentence would be "İlkbahar çok güzeldir." (not -dır) due to vowel harmony.