In some American or British dialects, are there entire words which can differ from standard proposed language, or is it only accent ?

The meaning of the word "dialect" says that words and phrases and grammatical forms which are "non-standard" are used by the speakers of that dialect.

A user of dialect will always speak with the accent associated with that dialect.

A person may speak "standard English" but with an accent.

Yes. See:

https://en.oxforddictionaries.com/usage/british-an...

Yes

No

There are words that are entirely different. For example, the compartment at the rear of the car in America is a "trunk," but in the UK, it's called a "boot." The lid that sits above an engine at the front of a car in America is called a "hood," but in the UK, it's called a "bonnet." A commercial transportation vehicle that hauls goods in America is called a "truck," but in the UK, it's called a "lorry." The liquid you put into a car to make it's engine run in the US is called "gas," but in the UK, it's called "petrol." The little room you walk into that moves people and things up and down to and from the various floors of a building in the US is called an "elevator," but in the UK, it's called a "lift." The sport of FIFA in the US is called "soccer," but in the UK, it's called "football." The little house you can hook up to the back of your car and haul around to various places to stay in in the US is called a "camper," but in the UK, it's called a "caravan," while in the US, a "caravan," is a procession of cars following a leader. In the US, when you "stop over" at someone's house, it means you went there for a visit, but in the UK, it means you spent the night there and didn't leave until the next day. There are many, many word differences, but not so many that we don't understand each other.

There are also words that are spelled differently. "Color" in the US is spelled "colour" in the UK. "Program" in the US is spelled "programme" in the UK. "Aluminum" in the US is spelled "aluminium" in the UK. So there are likewise many, many words with spelling variations as well, but again, not to such extent that we don't understand one another.

In British dialects, different words can be used. To give just a couple of brief examples, in Yorkshire they might say "Aye" instead of "Yes", or they might saying "Th'art" (= thou art) for "You are". Yorkshire and Lancashire folk might say "thine" instead of "yours".