How to improve your language skills as a translator
A good translator should have exceptional skills in both the target languages and the source languages. The most effective way is to enlarge your vocabulary - focusing on the words you encounter in your translation projects. The specific ways are as follows:
Build Your Own Dictionary
Read in full the dictionary entries for each word. Use several sources and bilingual dictionaries, both paper and online: If your monolingual dictionary gives a meaning that is not covered in your bilingual dictionary, start to research how that specific word and meaning could be translated. Take notes of the example sentences given in the dictionary, and think how you could translate them.
Study a word from the world
Don't limit yourself at searching in dictionaries: consult also encyclopedias and other reference works: See how the words are used in context in a variety of situations. Also, online tools can be very helpful to see how the words you are studying are used in the real world, both in books and in web pages and documents: You should also think about what they mean in your source language and what their translation mean in your target language. How the meanings differ between the two languages, and how register, connotation and usage differ between the two languages.
The importance of keeping notes
Remember, every time you translate something, take careful note of all the words that you are uncertain about of that leave you with doubts: the words you are not sure what they mean, and those you know what they mean - but you don't know how to say the same in your target language. They are the starting points for further research.
Keep on doing these, as much and as thoroughly as you can, you'll see that your command not only of your source language, but also of your native language, will steadily improve.