Why is the mother-tongue principle so important?

The mother-tongue principle with regard to translation means that texts are translated from the foreign language into the mother tongue. Therefore for example a Russian native speaker would produce a German-Russian translation and a German native speaker would produce a French-German translation.

Everyone has a better grasp of their mother-tongue than any language acquired in school, university, or by living abroad. (One exception to this is those who have grown up bilingual.)

It is widely thought that almost everyone who acquires a foreign language says: 'I cannot speak the language that well, but I am much better at understanding it'. The reason for this lies in the difference between active and passive vocabulary.

Also, trained and highly experienced translators are better at 'reading between the lines' in their mother tongue, and can capture subtexts and subliminal messages in the context of the culture of their homeland. These abilities are not only important in literary translation but also in advertising, since here messages should often be transported beyond the pure meaning of a word, and one plays with words or devises creative new concepts beyond the everyday - or the technical language. Expert language proficiency in a mother tongue is also important when the translator is tasked with translations for special target groups. Specialist vocabulary and slang terms can often not be found in any printed or online dictionary.

In every language there are a vast number of subtleties and characteristics that anyone who acquires the language over the course of their adult life will have a lot of trouble with: jargon, swearwords, regional expressions, slang terms, dialect and linguistic fashions. Someone who has grown up with this language and in this culture is able to provide the necessary quality as a translator. Someone without the target language as their mother tongue is generally not as able.

Why is the mother-tongue principle not sufficient on its own?

A stylistically as well as grammatically and orthographically sound translation is guaranteed through the mother-tongue principle. Subsequently the translation must be proofread by a translator in whose mother tongue the output text is written. Thus it is verified that the content of the translation is correct, and the nuances of the output text are successfully captured.