Do people in your country put sweater or blouse into the pants or no?

sweater, no
blouse, yes

Blouses yes, but not jumpers.

Probably because your hips and midsection tend to look odd and lumpy when you stuff your jumper into your trousers.

Some people do and some other too. More often with blouses, and in late years it has been a trend with sweaters, but only few people do it and I don't know how they do manage to make it look good

Old men and than wear their pants in such a ugly way that their fat beer belly hangs on top