Language is all about association: the association of meaning with
sounds or groups of sounds (otherwise known as words), and the meaning of words
in association with the context of their use.
Dictionaries can give a false picture of the ease with which one can
go from one language to another
equals-sign can seldom be set between the meanings associated with a word from
language and those associated with a word from another
language. The only clear exceptions to this rule are the numbers above
one. And some meanings simply cannot
be translated fully from one
language to another.
It is also easier to understand a language than to speak it, to read it
than to write it. So the people who have the best chance of making
sure that the meaning of a translated or corrected text is as close as possible to
the original are themselves native speakers of the target language.
They are also the people who are most likely to be able to put sentences together
in a way that sounds right to other native speakers.