I’ve studied English, Swedish, German, Spanish and Russian, in that order. My second language, English, was the easiest by far, although I suspect if I had started Spanish at the same time, it would’ve won (I progressed in Spanish much quicker with less work than in any language besides English, it really seems a friendly one). Other than that, subsequent languages have not been progressively easier -quite the contrary. German was hard, and Russian the hardest, by a mile.