You often hear of a “dizionario monolingue” (monolingual dictionary), a “dizionario bilingue” (bilingual dictionary), or of “traduzione multilingue” (multilingual translation) in Italian.
What seems to be forgotten, however, is the proper use of adjectives such as: monolingue (monolingual), bilingue (bilingual), trilingue (trilingual), plurilingue (plurilingual), etc…
First of all we should specify that the singular form for all the adjectives mentioned above, is “-lingue” and not “-lingua”. The term “monolingua” (monolingual) is only used as a noun – rarely used, moreover – with the meaning of “language or style which is intended as unique and unitary, like courtly Italian” (as described in the Grande Dizionario Italiano dell’uso, by Prof. Tullio de Mauro, currently professor of Linguistics at the University of Rome). It is incorrect, therefore, to talk about a “dizionario monolingua” (monolingual dictionary), an error which is often perpetrated by native speakers – and not just in the corridors of secondary schools.
However, the issue becomes tricky when you try to shed light on the most correct plural form:: “monolingue” or “monolingui”? If it is true that the singular of those adjectives ends in “-lingue” (lingual), is it logical to think that its plural form remains the same … or is there a plural version ending in “-lingui” (lingual)? The answer is not as obvious as it seems.
An article published in the “Scioglilingua” column of Corriere della Sera.it, tries to shed some light on the issue. In particular, among the various sources cited, the discrepancy between the online version of the Treccani dictionary (which defines the adjective as invariable) and the paper version (which gives the example of»dizionari bilingui«“bilingual dictionaries” was highlighed).
Tullio de Mauro talks about “Stati plurilingui” (plurilingual states) and groups of populations “trilingui” (trilingual) in a special section devoted to dynamics of contemporary linguistics published in the online Treccani Encyclopedia. These statements support the second hypothesis set out above.
The Accademia della Crusca (Academy of the bran*) tries to provide an answer to this question by comparing the most authoritative sources on linguistics (Treccani, Devoto Oli, Zingarelli, Sabatini Coletti). However, what emerges is an ambiguous picture full of discord. Some sources speak about the invariability of the adjective (as is the case with Sabatini Coletti), others accept the plural form “-lingui”, while the Zingarelli dictionary maintains that both versions are acceptable, without taking a clear stand.
For its part, Word spellchecker considers the adjective invariable. It is always advisable, therefore, to carefully re-read the text in order to avoid an untimely publication, because often the pitfalls lurk where you least expect them.
*The Accademia della Crusca (Academy of the bran) is an Italian society for scholars and Italian linguists and philologists. The aim of the society is to maintain the purity of the Italian language. Crusca “means” bran in Italian, which conveys the metaphor that its work is similar to winnowing.