Fabian: I undertand what you're getting at. I think your best bet, really, is simply to eschew the use of "you" completely in those instances if you feel confusion might arise. I'll show you what I mean:

In China you use chopsticks instead of forks ====> In China people use chopsticks instead of forks.

In Britian, you keep to the left when driving =====> In Britain, one keeps to the left when driving.

In Canada you need to dress warmly in winter ====> In Canada, one must dress warmly in winter.

Do you need a car in Los Angeles? =============> Is a car necessary in Los Angeles?

I've provided very simplified examples here, but this should give you the idea; basically, just re-phrase or re-structure the sentence to avoid the use of "you" when you want to avoid plural/singular abiguity. Does this help? If you need further clarification let me know.

it can be understood from the whole sentence and the meaning of situation 

also some words may indicate it's plural like when i say 
(All of you ) -(some of you )

and sometimes it may indicate its singular like (You are "a" good boy ) 
the "a" indicated it's singular  

Fabian,

Your question seems to be: when I'm talking about manners or traditions, I want to say "you (a group like country/region/family/organization) often do (something)"

There are many ways to do this in English, and some are more formal than others.  Some examples of referring to a group of people:

In Italy they eat lots of pasta.

In Italy people eat lots of pasta.

In Italy one eats lots of pasta.

You Italians eat lots of pasta.

If you say "in Italy you eat lots of pasta" it is ambiguous because you don't know specifically to whom you refers.  It could be you Italians, you as an individual visitor, you as a group of tourists, etc.

I think drive in England is not a good example because drive on one side or on the other is not an option. If everyone drives on the left you must do it too.

If I say "In England, you drive on the left."

You can't reply "no, here everyone drives on the left but I drive on the right because I like it"

If you clearly state the condition, or group of people, the "you" construction is more natural; "one..." is more formal (although easier to construct).

Different situation: "In England, you drive on the left." ("In England" makes clear you're talking about a hypothetical).

Goup of people: "In the Army, you make your bed every day." ("In the Army" makes clear you're talking about people in the army).

Advice: "If you have an older car, you need to take very good car of it." ("If you have an older car" makes clear you're giving advice in general to people in that situation.)

If you make it clear that it's a hypothetical situation, a different group of people, or advice, the "you" construction will work.