Why do we call toilet differently on different countries/cities?

lol. You forgot the Head and the Loo.. I think most people will be able to figure out what you mean if you ask for it while crossing your legs and dancing about a bit!

And here I still don't get it why we called it the comfort room. lol

In the UK you would ask for 'the ladies' or 'the gents' or 'the toilets' if you were in a public place like a bar or a shopping mall. In a private house or an office it would be more usual to ask for 'the loo' which was originally short for 'Waterloo' (a famous historical battle and also the name of a railway station!) which was used in polite company as a 'code word' for 'Water Closet' (also shortened to 'W.C.') What a long and involved history there is behind the names for such basic facilities - and all because of people's embarrassment at having to admit to performing natural functions! In Malawi (East Africa) my nephews learnt to call it 'the chim' which is short for 'chimbuzi' meaning 'the place of the goat' (presumably because of the smell!).

because idioms and jargons vary from country to country..

I would also wonder why is that. But I know in the airplane or ship there are some technicalities why they call it that way. However on different country I dont know and have no idea why is that.

Actually, they are just called differently depending on their purpose. It's true though that it's called restroom in the other countries. Anyhow, powder room is just for quick making up, lavatory I think is the political term for restroom, and the john is just a colloquial word. It's really called the same in almost everywhere. There's just many colloquial words. Don't get confused.

Hello damned idle, more Like Comfort Room for us yes. well, other countries have their way of telling what is the toilet, some prefer it as wash room too. too bad i couldn't recall other names being called to the toilet, maybe we could call it the "dumb zone"