Really interesting topic because I have the same questions than yours. I want learn two languages as the same time. English, mainly and in a second time I’d like to improve my Fusha skills (I have an intermediate level in Arabic). I don’t know if it’s a good thing to study two languages as the same time because it’s twice more time. Even my arabic level is more high than my English level, I know that it needs a lot of time (vocabulary, grammar, practice...). In an other way, I was interested to learn as a beginner Turkish but I don’t know if it’s a good idea... I know just some words and sentences in Turkish, so, it will need more time than improve my Arabic skills. To conclude, I don’t know it depends of you, if you have a good organisation and a lot of time ! In my case I think I will do it separately : focus in English for 2 months or something like that, then, improve an other language and keep studying English.