Translating both ways
Arabic · Key Stage 3 · The School
A plain Arabic verbal sentence puts the verb first: كَتَبَ الوَلَدُ الرِّسالةَ. Word by word that is wrote the-boy the-letter, which is not English. English wants the subject first, so the natural translation is the boy wrote the letter. Going the other way, an English sentence handed straight into Arabic word order produces something a reader will understand and no writer would produce. The first job in either direction is to find the verb and move it.
Arabic marks case on the ending: الوَلَدُ is the subject and الرِّسالةَ is the object, and you can tell without any word order at all. English lost those endings centuries ago and now uses position instead. Arabic also has a dual, a separate form for exactly two, where English can only say two of them. Every one of these is information that exists in the Arabic and has nowhere to go in the English, which is not a failure of the translator.
بَيْتُ الوَلَدِ is two nouns placed together — literally house the-boy — and it means the boy house, or the house of the boy. This is the IḌĀFA, and the relationship is carried by the grammar rather than by a word. English has to insert something that is not in the Arabic: an of, or an apostrophe s. So the English is longer and contains a word the original never used, which is normal and worth noticing rather than hiding.
Take ذَهَبَ الطّالِبُ إلى المَدْرَسةِ. The literal gloss is went the-student to the-school. The natural English is the student went to school. Now translate that English back into Arabic without looking. Most people produce الطّالِبُ ذَهَبَ, subject first, because English word order has stuck to the sentence on the way through. Compare the two Arabic versions: yours is a nominal sentence with a different emphasis, and the original was verbal. Both are grammatical. They are not the same sentence. Translating back is the cheapest test there is of what a translation quietly changed, and it costs nothing but a second pass.