Let's say I know Haskell and I'm learning Scala? Could I ask "I'm trying to accomplish X in Scala, I couldn't get it working. Here is the Scala I wrote that either I don't think is idiomatic, or isn't working, or is incomplete because I'm missing information Y. But here is how I would write it in Haskell. What is the idiomatic approach to this problem in Scala?"
No, that sort of question would not be on-topic here. It might be on-topic at StackOverflow, but you need to make sure that you come up with a SSCCE (Short, Self Contained, Correct, Example) for your question.
No. This site is about software development concepts – think software architecture and design. We are not a code translation service. We do not cover implementation issues. We do not discuss best practices.
If you frame that questions about how a language-agnostic concept (e.g. type inference, or monads) manifests itself differently in Haskell and Scala, that might be on topic. But it also might be closed as opinion-based, because it could be misunderstood as asking which language is better. You would also have to take care to keep the question clear and answerable (real questions have answers!), rather than trying to start a discussion.
This can be difficult, so it might be worth looking into our chatroom The Whiteboard. There, you can get feedback on potential questions. But it's also a place for softer questions that do not fit within the scope of the main site.