I wonder if English and Norwegian is even easier to mess up between them, than say Swedish and English. I have often thought that English and Norwegian seem closer to each other than Swedish and English, even though Norwegian and Swedish also are very very similar.
I am thinking of things like "great" and "accurate" and a lot of other words which are basically the same in Norwegian and English.
There are a lot of cognates between English and Swedish too of course, but often you have traverse the language a bit farther to find the root, and often there are subtle differences in meaning.
Purblind being my current favorite - meaning completely blind in Swedish and the same in English - but only archaic language! In contemporary English it apparently means "partly blind".
Besided, I really wonder about your example. "Låt gå för det" is a totally Swedish expression, AFAIK it's not translated from English. To my ears, it's a bit archaic, which would rather suggest that this idiom has a common germanic parent for both English and Swedish.
Remember, English got a LOT of its shape from Old Norse. (From Norwegians and Danes.)