What equivalence can and cannot promise
A translation substitutes for a source text, but equivalence can concern words, grammar, the text as a whole or its use in context. Fidelity to meaning does not require reproducing every source-language structure.
Translation and substitution
Translation can be defined as the process of rendering words or text from one language into another, or as communicating a source text's meaning through an equivalent target-language text. English distinguishes translation of written text from interpreting oral or signed communication.
The word translation derives from Latin translatio, to carry or bring across; Romance languages also draw on traduco, to lead across, and Germanic languages (except Dutch), as well as Slavic languages, use calques of these Latin sources. Other historical formulations include a turner in ancient Sumerian, to put across in German, to lead across in Russian and to turn in Latin. Greek metaphrasis, a speaking across, gave English metaphrase, a literal or word-for-word translation, contrasted with paraphrase, a saying in other words. In more recent terminology, metaphrase corresponds to formal equivalence and paraphrase to dynamic equivalence.
Translations substitute for texts in languages their readers cannot read, giving access to works otherwise unavailable to them. Assessing whether a translation is the same as, equivalent to or as good as its original requires understanding both.
Alternatives to translation include learning other communities' languages, adopting one common language or ignoring those who do not speak it; a world with about 7,000 languages in 2013 made learning them all impractical. International English can function as an escape from translation, although much of it has already been translated from the writer's native language.
Levels and limits of equivalence
Equivalence is contested: one view calls it an illusion because equivalent means virtually the same thing. Other views treat it as the conceptual basis of translation or as something artificial that translation itself must produce. The term can also be used for convenience because translators are accustomed to it, without claiming theoretical status for it.
Both the source author and translator bring cultural and linguistic conventions, readership expectations, aesthetic and formal considerations, knowledge, experience, outlook and attitudes to an assignment. Each assignment brings together a distinct pair of people pursuing a particular purpose in their respective environments, allowing many possible ways to produce equivalence.
Equivalence can be considered at word, grammatical, textual and pragmatic levels, but true equivalence or invariance is rare even at word level. Standardised nomenclatures can often achieve invariance: treating anatomical terms as Latin words in Terminologia Anatomica avoids the need to translate them.
Preserving a text's foreignness poses a further choice: Kafka sounds like Kafka to a German reader but may also sound German to a foreigner who knows the language without inhabiting it. Transmitting that foreignness is a real option only where the receiving language and culture have an established relationship with the source language.
Fidelity to meaning and function
Literality has traditionally been equated with fidelity, but fidelity can mean fidelity to meaning, and excessive literality can work against it. Source-language structures need not be replicated to obtain the same effects, including legal effects.
In one biomedical translator's view, untranslatability should not be a problem for scientific and technical translation: some nuances may be lost, but they are usually irrelevant to the broader picture, or should be. A good translator can convey all the source text's semantic content in a functional equivalent despite linguistic changes. Functionalist approaches associated with Reiss, Vermeer and Nord offer a way to understand and manage this problem.