A longer answer would be that English is descended from the Anglo-Saxon language, which is even more similar to the Norse languages (Swedish, Danish, Norwegian, Icelandic). Old English also got an injection of Norse influence from the Viking invasions of England in the 9th century.
They are basically the same, but different dialects prefer different constructions. I prefer denna/detta for example, but I know that for many, den/det här feels more natural.
It is important to remember though that detta/denna is followed by the indefinite, and den/det här is followed by the definite. e.g.
Denna bok - This book
Den här boken - This book
Some dialects accept "denna boken" but that is not generally accepted.