"Él quiere unas frutas."
Traducción:He wants some fruit.
If you are talking about several different kinds of fruit, it is generally acceptable to use fruits. For example. strawberry, raspberry and cranberry fruits is an instance of this
This is tricky to explain, because there are few strict rules about which nouns are countable and uncountable, so I will hope you will forgive this over-simplified account:
Some nouns (e.g. chair) are countable. We can say "one chair", "two chairs", etc. They have singular and plural forms. Other nouns are uncountable. We do not say "one fun" "two funs". There is no plural form of fun. Many nouns have both countable and uncountable senses. E.g. you can have a bar of chocolate [uncountable], or a box of chocolates [countable, plural]. Nouns for classes of foodstuff (fruit, meat, cheese, etc.) are usually uncountable, but they take a countable sense when we talk about different varieties (a wide selection of cold meats and cheeses). Your example sentence talks about different varieties of fruit, so fruits is fine