I haven't reviewed any Kotlin codebases. My guess is that if people choose Kotlin then at least they had some opinions on languages, so I'd expect more. But as

I haven't reviewed any Kotlin codebases. My guess is that if people choose Kotlin then at least they had some opinions on languages, so I'd expect more. But as I said, that's just a guess. On average Java codebases I have reviewed tended to be slightly better than the C# codebases. The C# codebases I've seen have tended to be more "garden variety meh" while Java tend to be either south or north of "meh" - if that makes any sense. They're more often either terrible or fairly nice. Though I've been lucky and seen more nice than awful Java. (There is a separate circle of hell for Spring and other metastasizing frameworks). That being said, the all-time worst codebase I have reviewed was in Java. An EMV system written in a hurry with almost zero error handling.