There are a lot of ways to look at it. I think [1] is one of the better attempts and would suggest that the spread is much bigger for average jobs than for the highest paying positions, and that e.g. Scala, Rust, Perl or Go will earn you more money than Dart, JavaScript, PHP or Java. Also apparently jobs with DynamoDB pay almost twice as good on average (median) as jobs with Firebase; and Postgres or MSSQL pays better than MySQL or Oracle.

1: https://stribny.name/blog/salaries-by-language/