I disagree with the migration of my question: https://german.stackexchange.com/questions/18895/learning-german-and-yiddish-at-the-same-time
In asking the question, I was hoping that readers knowledgeable about language acquisition could make plausible inferences about my situation from what is known about speakers or learners of two languages whose proximity is comparable to that of German and Yiddish. For example, if someone was aware of a study on people learning Spanish and Portuguese simultaneously, that would be highly useful. That may be better than anything I can hope for, but as I said, at minimum I am asking for plausible inferences from what is known about language acquisition.
The migration has instead narrowed the question to one about a specific pair of languages that few people are likely to have useful information on. I don't see how the German site will better be able to address the issue of what one should consider in learning two closely related languages.