Learning Two Languages Together: Where are the Resources?

Remembering new vocabulary involves a lot of connections between what you already know and what you want to know. This is why I don’t agree with “target language only” classes. Sometimes you need your native language to help you  learn a second language, and sometimes a second language can help you learn a third language even better.  For example, learning German in French is actually easier for me instead of learning German in English even though German and English are more closely related.  Whenever I try to think in another language and want to say something, French is what comes out first because it’s my second language. So now I think in French first for a few seconds before I can switch to German. It’s just simply easier for me to go from French to German than from English to German.

Whether you are learning two languages together and are at the same level in each, or whether you know one language rather well and are using it to learn the other, having the grammar and vocabulary compared side by side is a useful resource. This is why I decided to start writing comparative tutorials. So far only French & German and French & Italian are available, but I would like to do French & Spanish and Spanish & Italian someday. I don’t know of any language learning books that do this apart from the English Grammar for Learners of…. series, but that is always English + one other language, and I am trying to find resources for learning two languages simultaneously that is geared towards English speakers. But perhaps the market for learning two languages is not very large since most people seem to think learning one language is hard enough. But what about the multilingual enthusiasts like me? Or graduate students who must learn two languages in order to finish their PhD? Surely there are resources for students in a Romance Languages PhD program? Or are those books only available in graduate libraries?

I know there are plenty of multilingual phrasebooks for travelers, but I’m looking for introductory books that teach basic grammar and vocabulary of two languages (any combination, really) side by side. It seems to me that a book on learning Spanish and French together would exist since those are the most commonly learned languages in the US, but I cannot find this book. Does anyone know if something like this actually exists?

Luckily, I have some other multilingual comparative books, and I’m keeping a list here if you’d like to buy them too.