Twitter isn’t a phone call, but it also isn’t a message board. You only see the tweets of the people you personally choose to follow; it doesn’t matter if there are 100 billion spam accounts posting ads to nobody.

There are millions of Twitter accounts in Japanese, but if you don’t follow any of them, and nobody you follow retweets them, you’d never know they exist. You can also block or mute specific accounts, mute keywords, etc for even finer control.