Japanese people say "delicious" far more often than native English speakers do. In Japan, where I lived for about 6 years, I was surprised by how often I heard the word. When I spoke to other native English speakers, everyone seemed to feel the same way. Why is that?
The reason is that delicious is a direct translation from a Japanese word (美味しい), and that word is very commonly used in Japanese. However, just because a word is used in one's native language, it doesn't mean you should always use a direct English translation.
It is correct to say, "It is delicious." However, native English speakers usually don't say that. There is no special reason, but they prefer to use a superlative like "amazing", "great", "so good" etc. Native speakers will also use sense verbs like "taste" or "look", so:
A: That cake looks so good.
B: Yea, and it tastes amazing!
C: It's incredible. I love it.
This brings up the deeper point: just because you can say something, should you really say it?
No. Translating directly from your native language is a big roadblock when you are learning a language. Instead, ask what a native speaker would say and try saying that. You will sound a lot more natural, and you will begin the journey of understanding foreign culture and real communication, not just vocabulary.
So, to begin with, try not to say "delicious". Instead, say the food looks so good or it tastes incredible.
a big roadblock - something that will stop you from achieving a goal