Haha, the thread brings back memories.
The first two foreign languages i took were French and Spanish and I had the hardest time seperating them. I would fuse words together from both languages, interchange grammar rules, absolutely killed both languages. I would say things like J'estoy content.
anyone that knows both languages, wud understand how stupid that sentence is. anyways, later on i took hindi and german together and had absolutely no problem grasping both at the same time. so i think that as long as you take two distinct languages they do not interfere with one another. later i took chinese and russian together, then turkish and tamil together, and currently im focusing on written chinese along with japanese and its getting pretty confusing again because of the kanji thing. my brain keeps reading the kanji in chinese and the attaching the kana at the end, so everything sounds rubbish. however, i stil lfind it beneficial to learn both at the same time.
im not sure y, but as u start getting a grasp on learning how to learn languages, and linguistics, i think it becomes easier to learn languages. i guess it just a broader spectrum of things u can compare what ur currently learning with. anyways, thats my two cents.