Dual Language Course
I've had this thought for a while now. What do you think about getting taught two languages together? I'm not talking about two separate courses. One course teaching two languages. For example I'm learning Japanese and French. So after I learn a Japanese word, instead of using English again to learn the French word, I use Japanese. (eg. I learnt Fish = Sakana. Then Sakana = Poisson) I think that way I can focus more on those two languages instead of thinking about English. So a course aimed at teaching two languages at the same time. The process could go something similar to how I try to fade out the English word once I know it in one language and use that to learn the word in the second language. Same for sentences. Opinions?
It's called laddering and easily done with Duolingo. You can go to the courses for speakers of one of the languages that you are learning. I think that it helps if you have at least some minimum skills in one of the languages. Many Duolingers seem to wander over to courses for speakers of other languages, then get stuck there as they can't read well enough to navigate their way back.
I've done it a bit of laddering such as the Portuguese and French courses for Spanish speakers. After I finish with my Portuguese tree, and then Japanese, I'll probably go back to finish those at some point. For me, it's been helpful to do the Spanish reverse tree first before laddering, but some people might be confident enough to do laddering directly.
I've done something similar to your notes with my Portuguese tree. Often it's fairly obvious what a word means and I don't need to check the hints, but if I do need to peek or my guess is wrong, I usually write down a translation in whatever language seems most similar. For example castelo = castillo.
I also sometimes put on a movie in say Spanish but use the French subtitles if Spanish subtitles aren't available, or use Spanish subtitles for a Portuguese movie. It's not ideal, but I figure that it's better than using subtitles in my native language.
Something similar you can reach by doing "reverse tree", when you have enough competence in a foreign language. In my case, I do French from English and English from French in order to learn or to improve both languages.
I have discovered that is easier "to switch" from a foreign language to another instead to switch from mother tongue to foreign one.
Sadly, there are not available yet Japanese from French or French from Japanese, but imho is a good idea.
It works great, that's exactly what I'm doing. I'm a native English speaker, but the flags on my profile are NOT from English (except for some of the lower numbers like Japanese and Dutch, etc. that I was just toying with.) My German and Italian flags are both from French, and my French course is being learned from German. The Portuguese course I am doing in both French and English. Only one number will show up next to each flag on your profile, showing the highest level you have reached in that language, no matter what was the base learning language. My English based courses no longer show up as numbers because I finished the tree in English but started using other languages to study from when I discovered that was possible. I love laddering!
I don't think the site technology is there yet. I have contemplated in taking Spanish as a French speaker as my French is stronger than my Spanish. It is an interesting concept. I think as programming goes they would have to let you select more than one site language to create a dual choice.