Tack, tack, tack & Sumimasen!

The most common word in Sweden is probably TACK (thanks). In Sweden you hear Tack, tack, tack all the time. The Swedes seems to say thanks whenever there is a slight reason for it. I don't know the reason for this excessive use of Tack. Maybe it is a way to excuse for making trouble, in a sublime way. "Tack" for pouring my glass of water in a restaurant meaning “sorry for making you trouble”... even though the waiter is actually hired to pour my glass and I pay for the service.
The most commonly word used in Japan is probably SUMIMASEN. You hear the word all the time and the meaning is “Excuse me” or “Sorry”. Sumimasen is said initially, when you ask someone something. Or Sumimasen for not letting someone to do smth, that you actually consider would be a bad idea (like taking your chair). Also you say Sumimasen instead of “Thank you” when you might have caused someone little trouble. Like the shop assistant giving back money for a purchase says; “Sumimasen”; meaning: thank you but sorry for bothering you giving the exchange back (!)