In 4 years, you can reach basic fluency in Japanese, but you'll have to work hard. Since you're gonna become a translator, you'll be required to learn properly the grammar (which isn't really difficult, japanese grammar is indeed simpler than english) and at least 3 thousand characters. I don't know anything about universities in Turkey, but I'm pretty sure that even if classes will be held on a very high level you won't be able to master this language in just 4 years if you rely just on what you'll be taught in class: you'll have to work a lot by yourself.
Things will be simpler if you choose english. There aren't all these characters to learn, and since you already know the basic grammar, 4 years of practice are more than enough to become fluent in English...
As for your work... I guess there are a lot of turkish people who are fluent in english, but how many turks speak japanese? Not a lot, I guess. Probably, if you choose japanese, you could have more job oppurtunities.
However, good luck for your exam!

No one can make this decision but you. No one knows if you can learn Japanese or not. Unless you know you are a very natural language learner, you will not know whether or not you will like taking Japanese or not.

I know people whose dream was to learn Japanese and live in Japan. They began studying and quit after 2 weeks. On the other hand, I took Japanese just for fun to share a class with my friend. He quit after 2 years, but I continued and now am a translator.

You can choose Japanese, but Japanese also has to choose you.