The back-translation (sometimes called retroversion) is to write back in the language of a text already translated. It can be a very accurate and useful work as one who is translating English text into French and then retranslated into English: thus verifies the conformity of the two versions and can be corrected in the original text of ambiguous formulations that have resulted in errors in the other language.
The proper use of back-translation
Apart from the case where it is possible to control the outcome, the back-translation can be helpful but one should be aware of its limitations for what can be found is always tainted with uncertainty. A Russian text of Marc Bloch and gives us his thoughts: “Я еврей, – писал Блок, – но не вижу в этом причиныни для гордыни, ни для стыда и отстаиваю свое происхождение лишь в одном случае: перед лицом антисемита.” Russian translator was quite right to use the quotes because everyone knows that he had written in the language of Voltaire and not in that of Pushkin, however the French translator would be an abuse if he gave us, for example: “Je suis juif, écrivait Marc Bloch, mais je n’y vois pas un motif d’orgueil ni de honte et il n’y a qu’un seul cas où je proclame mon origine : quand je suis devant un antisémite,” since the quotes attest that these are the exact words the great historian when nothing assures us. In such cases it is necessary either to prefer indirect speech: “Marc Bloch écrivait qu’il était juif mais qu’il n’y voyait pas etc.,” or search the source in French (ie L’Étrange Défaite) really written that: “Je suis juif […] Je n’en tire ni orgueil ni honte […] Je ne revendique jamais mon origine que dans un cas : en face d’un antisémite.”
Subject to this, the back-translation is often used on an ad hoc basis to resolve a problem. English text written by a German speaks of “high school”, while obviously it is just a higher education institution; it can be assumed that the German writer thought “Hochschule” and had been the victim of a false friend. It will therefore translate accordingly while remaining cautious and warning the client by note.
The same caution should ban to state conclusively that a text is a translation because it appears features from another language. The monumental Histoire linguistique de l’Alsace-Lorraine of Paul Levy is dotted with Germanisms because the author, born in the German Alsace, had studied at the time of Reichsland, but no one has ever thought to pretend that there existed a German original and try to reconstruct it. Such fun is for older texts for which there is little chance that the discovery of an original manuscript come to ruin beautiful constructions (like Pagnol has given in his play Jazz a fun example).