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As other have said, this is correct but: 1) I want to improve my English because I will need it for my future job. (General statement) 2) I need to improve my English because I will need it for my future job. (Changing want -> need, you are showing ‘pressure.’ You must work on your English now, otherwise your future job will be challenging). Good luck! I very recently started learning Arabic. The languages are so different!

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Welcome! Hope we can help!

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This is grammatically correct, but it sounds like you have already been hired for a job and you will start soon. If you mean that you will need it for a job that you don't have yet, you might say: I want to improve my English because I will need it for work.