Many people worldwide who have learned English as a second language use a British accent when they speak English. But Scandinavians, especially Swedes, often appear to sound American. Some Swedes can even pass as Americans, with only a slight accent to an untrained ear.
Swedes and other Scandinavians sound American because they consume a lot of American-made media. A Swede who prefers British television will probably sound less American. While other Europeans might learn British English in school, Swedes often start learning English before they start school.
The accent someone uses in their second language depends on their teacher and the accents they hear in that language. Young Swedes watch a lot of British and American television, which helps familiarize them with the English language.
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Why Are Scandinavians Good at English?
English is a difficult language to learn, but Scandinavians have an advantage over other Europeans. English has more in common with Norwegian, Swedish, and Danish than most other European languages, making it easier for Scandinavians to learn.
Scandinavians are good at English because of the similarities between English and Nordic languages. They also tend to consume English media as children without translations.
A Forbes article on this subject also cites the professional advantages of learning English.  Scandinavians often study abroad and travel to hone their language skills. Young Scandinavians with dreams of entrepreneurship know that English is key to the global market, so it is common for them to become fluent.
One of the difficulties of learning English is that it has roots in Germanic and Romance languages. Many everyday English words have Germanic origins, while more academic words come from Latin. Rosetta Stone, the language-learning software, states that eighty of the hundred most common English words are Germanic. 
English is a Germanic language, along with German and Scandinavian languages. Because these languages come from the same family, it is easier for a native speaker of one to pick up another. Conversational English is more likely to use Germanic words that are already familiar to Scandinavians.
Scandinavian children start learning English long before it is introduced in their schools. Their first exposure to the language is as soon as they watch English television and movies. Scandinavians often use subtitles instead of dubbing to translate their media, so children hear their television in English.
With the help of subtitles and context clues, children can follow the meaning of their shows or movies without knowing English. Over time, they can pick up enough of the language to become almost fluent, even before taking English classes in school.
Common Swenglish Mistakes
Despite these advantages, Scandinavians do not speak perfect English. “Swenglish,” English when spoken by Swedes, contains several grammatical errors. Swenglish is understandable to an English-speaking audience, but it can sound a little strange.
Swedish YouTuber Katrin Berndt has a video on Swenglish.  She highlights some of the most common errors Swedes make in English. Some of these include mixing up “fun” and “funny,” “learn” and “teach,” and “lend” and “borrow.” In Swedish, these pairs of words are just one word each, leading Swedes to confuse the two in English.
Berndt’s video also highlights the English sounds that Swedes struggle with, including “ch,” “j,” and “th.” A Swede who struggles with these sounds will have a more pronounced Swedish accent, even though his or her vowel sounds might be consistent with American English.
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Do Norwegians Sound American When They Speak?
The same factors that help Swedes speak English easily, which might give them an American accent, also apply to Norwegians. Norwegians who consume large amounts of American media with subtitles instead of dubs are more likely to have an American accent.
Most Norwegians have a Norwegian accent when speaking English, but their pronunciation is more American than British. The exact accent depends on the person’s education and what media they listen to.
Like Swedes, Norwegians may struggle with some consonant sounds in English. The letter “j” can be pronounced as a “y.” Norwegians might enunciate their English words more precisely than a native speaker would, and they tend to raise the pitch of their words in a sing-song effect. As a result, Norwegians do not usually have perfect American accents and sound distinctly Scandinavian.
Norwegians might “sound American” as opposed to British because of how they pronounce their vowels and the letter r. Americans pronounce “r” more strongly than Brits, and Norwegians who speak English tend to follow the American pronunciation. Norwegian vowel sounds are also more similar to American ones than British ones.
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Do Danes Sound American When They Speak?
To someone who isn’t from Scandinavia, Swedes, Norwegians, and Danes probably all sound the same. Their native languages are quite similar, and they often make the same mistakes when speaking English.
Danes, like Swedes and Norwegians, have a Scandinavian accent when speaking English. Their English sounds more American than British, but it is still distinctly Danish.
Danes are usually very comfortable speaking English. According to the University of Copenhagen, 86% of Danes speak English as a second language. But they still have a Danish accent, unless they have spent a long time practicing to get rid of it. 
Like Americans, Danes are more likely to pronounce the letter r when it follows a vowel. They also tend to use similar vowel sounds to Americans rather than Brits. However, a Dane’s oral posture is not identical to an American’s, so there will naturally be some differences between American English and a Dane’s English.
Danish YouTuber Kelly Louise Killjoy displays her accent in a video highlighting differences in accents and idioms.  She pronounces words like “fire,” “oil,” “route,” and “again” as an American would. But other words like “sure” and “theater” come out more British.
A Norwegian YouTuber named Sunny completed the same “accent challenge” featuring her Norwegian accent.  The results sound very similar to an American ear. Both young women speak English very well, but they have definite Scandinavian accents.
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Scandinavians speak English very well, but they still sound Scandinavian. On average, their accents lean more American than British.