[adastra22]

In the same way that Swedish has two tones. Bitonal systems aren't quite as difficult as language like monosyllabic polytonal languages like Mandarin or Cantonese though. There are a handful of words in Japanese which are differentiated in pronunciation only by tone, but these are relatively rare. If you screw up the tone in Japanese it will sound like a bad foreign accent but you will likely still be understood. Just about every word in Mandarin on the other hand has one or more conjugate tone pairings, and if you screw up the tone you're speaking nonsense.

(Source: 10 years learning Japanese, followed by marrying someone from Taiwan.)