Learning a new language is definitely a challenge worth mastering. I will do my best to answer your questions. A.) There are a variety of tests available online you can take in order to determine where you need to improve. Here is one of them and it is free: http://www.cambridgeenglish.org/test-your-english/ B.) Honestly, the level of English you need to have depends on the company you choose as your place of employment. I work in Marketing for a very large global firm and as long as you demonstrate an above average level of English knowledge, you will allow yourself to be in a position to be hired. C.) How long it will take you to learn English depends on you. Only you can determine how much time and effort you will put into learning the language. Although, I have to admit based off of how you have formed your questions, you are well on your way to mastering the language. :) D. ) The best way to learn a language in my opinion (I am learning Spanish) is to practice, practice, practice! The best ways to practice are to read books, listen to music, watch television in the language you wish to learn. I also recommend taking classes offline and online. One of the main reasons I joined iTalki is to supplement my learning by practicing the language with other people. The more you practice the more you will learn. E.) In my opinion, the best way to determine your weaknesses is to see how much you comprehend when you follow the recommendations I listed in D (see my answer above). Also, if you are looking to practice with someone, I am a tutor on this site so please feel free to contact me as well. I hope this helps and best of luck! :)