Caution: I am not a native speaker, but I will try to answer based on what little I already know.
Indonesian relies mostly on context for this. Here, for example, it is pretty obvious that the sentence is about apples and oranges in general, otherwise the sentence would be something like: "Saya suka apel dan jeruk ini". apel ini, jeruk ini = this apple, this orange.
Yes, you're right.
It depends on the context.
If it's obvious from the context that you're talking about the plural form, then the plural form (reduplication) is not used.
Like in this sentence, it's interpreted as apples & oranges in general, so there is no need to reduplicate (apel-apel).
A more obvious example is this :
I have one book = Saya punya satu buku.
I have two books = Saya punya dua buku.
I have many books = Saya punya banyak buku.
Yes, that's right.
It feels like more fruit is coming ... the word "and" (dan) comes before the last fruit.
Something like this :
Saya suka apel, jeruk, pisang, stroberi, ceri, rambutan dan durian.
I think you're right.
It's an unfinished sentence.
This person simply couldn't finish the sentence with all that fruit.
Yes, that's my favourite fruit.
Durian is a little bit controversial, a lot of people can't stand the smell, therefore it's usually forbidden to bring durian into a hotel or public buildings.
But the taste...hmmmm...there is nothing like it.
Durian = King of Fruits
More info here about 'durian"
'duri' = thorns.
I thought for plurals that the word is repeated with a hyphen; e.g. apples = apel-apel.
Yes, that's right.
If reduplication is used to indicate the plural form, then the word is repeated using a hyphen.
But in this sentence there is no need for a reduplication to indicate the plural form.
The sentence (more or less) indicates that we're talking about apples & oranges in general.
So, we're talking about more than one apple.
So, no need for reduplication.
Here a tip: you can put every countable noun twice to show that is was plural
Ex: "Mobil Mobil" "Kuda kuda" "wortel wortel" etc. but its not work for uncountable noun bcos uncountable noun has no plural form. But you can use another form of a noun word.
Ex: you can't say "lot of water" as "air air" but you can say "botol botol air (more than one bottle full of water)" "ember ember air" etc. Although some native speaker still said "air air" to show more than two containers with water inside (no matter if it's was full or not)