The most important challenge for practical and theoretical
lexicographers is to define the functions of a bilingual dictionary. A bilingual dictionary works to help users translate texts from one language into another or to help users understand foreign-language texts. In such situations users will require the dictionary to contain different types of data that have been specifically selected for the function in question. If the function is understanding foreign-language texts the dictionary will contain foreign-language entry words and native-language definitions, which have been written so that they can be understood by the intended user groups. If the dictionary is intended to help translate texts, it will need to include not only
equivalents but also collocations and phrases translated into the relevant target language. It has also been shown that specialized translation dictionaries for learners should include data that help users translate difficult syntactical structures as well as language-specific genre conventions. In standard lexicographic terminology, a bilingual dictionary definition provides a "translation equivalent" – "An expression from a language which has the same meaning as, or can be used in a similar context to, one from another language, and can therefore be used to translate it." The British lexicographer Robert Ilson gives example definitions from the
Collins-Robert French-English English-French Dictionary. Since French
chien = English
dog and
dog =
chien,
chien and
dog are translation equivalents; but since
garde champêtre =
rural policeman and
rural policeman is not included in the English-French dictionary, they are not culturally equivalent. Both phrases can be understood reasonably well from their constituents and have fairly obvious contrasts with
garde urbain in French or with
urban policeman in English. But
garde champêtre has a specific unpredictable contrast within the lexical system of French: it contrasts with
gendarme. Both are policemen. But a gendarme is a member of a national police force that is technically part of the French Army whereas a
garde champêtre is employed by a local commune.
Rural policeman has no such contrast. Perhaps the most difficult aspect of creating a bilingual dictionary is the fact that
lexemes or words cover more than one area of
meaning, but these multiple meanings don't correspond to a single word in the
target language. For example, in
English, a
ticket can provide entrance to a movie theater, authorize a bus or train ride, or can be given to you by a police officer for exceeding the posted speed limit. In
Spanish these three meanings are not covered by one word as in English, but rather there are several options:
boleto or
entrada and
infracción/multa, and in
French with
billet or
ticket and
procès-verbal, or in
German by
Eintrittskarte or
Fahrkarte and
Mahnung/Bußgeldbescheid. Recently, an automatic method for the
disambiguation of the entries of bilingual dictionaries has been proposed that makes use of specific kinds of
graphs. As a result, translations in each entry of the dictionary are assigned the specific
sense (i.e., meaning) they refer to. Open-source software for generating bilingual dictionaries automatically is also available, such as the ApertiumBidixGen project. == Usage ==