"The boy is translating the article into Russian."
Translation:Мальчик переводит статью на русский язык.
My logic would have been more this:
The language is being placed INTO Russian, therefore prepositional.
Rather than this:
The language is moving from one language TO another, therefore directional.
But that is the logic of a native English speaker, and not relevant here — I just need to learn the logic!
When using the alternative versions of the demonstrative pronoun это (which typically means 'the'), such as эта and этот, the subject is emphasised.
<<это мальчик читает> - 'the boy is reading.'
<<этот мальчик читает> - 'this boy is reading.'
The English sentence provided by the question doesn't specify that this boy is translating the article, so это is used.