I had been mulling learning Scala or Haskell as an adjunct
Don't make the same mistake as me. Scala used to be the best language for big data and data engineering stuff. Spark api for scala were always a step ahead of the python api. But most projects have now realized that python is the better alternative for data engineering stuff so they are providing better support for python api of their libraries. Scala 2 to Scala 3 migration has also been a cluster fuck.