Patrik Laine is a bad example because he speaks exceptional English for your typical 18 year old Finn. He's very articulate and speaks better English than most Finns, period. Educated adult or uneducated kid. Tuukka Rask is another one who spoke almost flawless English when he first came over. These two don't represent the norm. They are rare exceptions.
Rask is definitely exceptional, but Laine is quite far from it. He can easily get his points across, but overall his language skills are average or only slightly above average for an 18 year old. But I can see him easily becoming very good after his first year abroad.
Currenly Laine is even bad compared to an average Finnish NHL Pro. Rask and Haula have pretty much no accent, but even the average guy there is quite good for example pretty much all the goalies are quite fluent. Just go watch interviews of Rinne, Ramo, Raanta, Lehtonen or Korpisalo. Even Niemi is passable and Bäckström was good even if he was older when he went over. Same goes for most of the skaters as well.
Remember, these kids don't spend the majority of their days on the internet, playing video games or watching movies on Netflix like the average Finnish teenager. They spend countless hours in their youth on practicing and playing hockey. It's not that peculiar that they don't get exposed to the English language nearly the same amount the average kid does.
I'm pretty sure they do the typical young kids stuff when they are younger. 9 to 12 year old kids don't just go pro. And I'm sure even pros watch tv and listen to music. No matter how talented they are they still go through the same motions as the rest of us.
I still can't understand how you can grow up dreaming of playing in the NHL, but then you completely neglect your language skills, which make the transition so much easier.