Is it wrong to say fruits?

See a translation

Both 'fruit' and 'fruits' can be used, but it depends on what you are saying.

If you mean fruit in general, as a concept, then it is always "fruit" even for plural.
1 pieces of fruit, 2 pieces of fruit, 3 pieces of fruit.
I bought a bag of fruit.
There was a bowl of fruit on the table.
Eating plenty of fruit and vegetables is healthy for you.

But sometimes you can use 'fruits' if you are talking about several different kinds/types of fruits:
The store sells different kinds of fruits: apples, bananas, strawberries, apricots.
The orchard grew several different fruits, but the apple and pear trees were my favorites.

But if you are not sure if it should be 'fruit' or 'fruits', you can usually just say 'fruit' and it will be fine. Using 'fruit' is a lot more common in most sentences, and will be understood.

You might find this helpful to explain why this word is like that: http://www.englishteachermelanie.com/when-is-it... It does a pretty good job explaining it in a little more grammar detail.