I don't speak English perfectly and I have a problem with it...
Like I said I don't speak English perfectly but if I want to learn English then I need to change language, but it don't have language from my country (Serbia) and I can only change to Spanish but it's not working so well because I actually learning Spanish on this website too... I don't know how can I learn English and understand what i need to do at the same time... If someone have a same problem or problem like that and if he/she found the answer please tell me because this website will help me a lot... I'm learning Spanish better, faster and easier than in school... Thanks in advance!!!
From your post above I doubt that Duo could be of great help. Your English while not perfect is probably far more fluent than Duo would make it. What you probably need a more advanced English course or just more immersion in conversational practice if that is available to you. You may also find www.abaenglish.com a useful site which includes courses at various levels of fluency. It is a subscription site but they also offer a free membership which gives you a chance to try it out first.
Unfortunately, it does not appear that Duolingo has any course from or for Serbo-Croat (or any of its dialects). That said, if you have a foundation in English, taking either English-Spanish course could help you improve both languages. Taking a course to learn two languages (without your native language) is not uncommon on Duolingo.
I'd encourage you to keep on with the Spanish from English course. I think your English is more than good enough to get a lot from it. You'll just learn some English along the way. As Cognocto said, many people use this sort of strategy on Duolingo to practice two languages at once. Even has a name: "laddering" (from "ladder"), idea being you're using one foreign language as a base to learn another foreign language.
Well you can go to Google translate to translate the word you don't know to Serbo-Croat.Writing the primar text of the blog, I can say you speak enough fluent. This post was made 1 yr ago, I guess now you are great in English! As for me I'm Albanian, and when i do not know a word's translation, go to google. Besides I know better English than my mother tongue!