Japanese has a common link with the Altaic languages; Korean, Turkish, Tungusic, Mongol.
In regards to tonation, i would deign to say that Korean is very close.
Altaic languages - Wikipedia, the free encyclopedia
So can you understand Korean without actually being familiar with the language? Swedish and Norwegian have different words, but the same syntax and semantic rules and pronunciation - thus if you know one you can understand the other. The words are similar too.
Norwegian:
Coastguard - kystvakt
Meatloaf - kjøttpudding
Highway - hovedvei
Oil - olje
Snow - snø
It's cold outside - det er kaldt ute
I think you're cute - Jeg tror du er søt
Swedish:
Coastguard - kustbevakning
Meatloaf - köttfärslimpa
Highway - huvudväg
Oil - olja
Snow - snö
It's cold outside - det är kallt ute
I think you're cute - Jag tror att du är söt
Similar, but not identical. Still, their similarity is close enough that a speaker of one can understand the other, even if you don't actually know the language.
Of the three Nordic languages (discounting Icelandic which is most similar to Faroese), Danish is the most unlike the others, it has different words but also some different syntax and semantic rules, speakers of either Swedish or Norwegian can still understand it though.
If you took a random Japanese and a random Korean person who didn't know each others language could they understand each other if asked to converse?