Use two ratings/scores to evaluate each translation — accuracy and fluency.
Accuracy would indicate how well your English translation reflects what was said in another language.
Fluency would indicate how fluent your English translation is regardless of accuracy.
In this way, learners would be encouraged to write fluent English when translating.
Moreover, this could be part of an overall effort to help you improve your command of the language that you already know while you learn another language.