When talking about fruit in general, you always treat it as an uncountable noun. Many learners make the mistake of just using "fruits" all the time, which makes me think that they they're not properly familiar with the language. "Fruits" usually means "certain kinds of fruit". You would not normally use this form unless you had a specific situation, or you were then going to list the types of fruit. "Apples are my favourite fruit" is the natural sentence here.

when you speak about different kind of fruits,you must use fruits but when speak about a specific fruit u must say fruit example:apples are my favorite fruit I think a word ''fish' is in this way,too'

Apples are my favourite fruit. ---> you have one favourite, it is singular so use "fruit" OR Apples are one of my favourite fruits. ---> you have many favourites, plural, apples are one of those, so use plural form "fruits"

Bonjour Un fruit (sans 's') singular Des fruits (with 's') plurar It's ok ?

I think it would be: Apples are my favorite fruit.What is your favorite fruit. ( When you are talking about a specific kind of fruit) I like fruits.Do you eat fruits? (When you are referring to different kind of fruits.) I hope that is correct.