concerning situations where the question's author asks for the most sound course of action in their particular language learning situation.
The first bold phrase screams opinion-based to my eyes. "Most" as a word already shows that the following answers will be subjected to opinions rather than facts. This is a big no-no in Stack Exchange let alone this site. For me, the most sound option might be option A while to you it's option B. This causes flame wars, a distrust between users within the community, and lots of chaos.
The next part means the question is too localized. The situation will probably only apply to very few people, which means that the question isn't going to be that helpful at all to the visitors. The situation presented within a question should be applicable to a lot of people. Take the current best (in terms of score) question: Are there any studies which address the effectiveness of studying multiple related languages simultaneously?
The situation here is learning multiple questions at the same time. We can safely assume lots of people do this or at least consider this as they try to acquire new languages.
Also, it ends with the classic hallmark of an opinion-based: "What do you judge better?"
The usage of "better" in the question is definitely marking the question as opinion-based. That's pretty self-explanatory.
These questions are not only opinion-based but too localized to be helpful to a good amount of people. Thus, these questions should be off-topic.