sesquilingualism

Etymology
From.

Noun

 * 1) The condition of being sesquilingual; the ability to speak one language fluently, and a second language only to a limited extent.
 * 2) * 1972 R. David Zorc, "The Western Subgroup of Bisayan," Oceanic Linguistics Vol. 11, No. 2 (Winter, 1972), pp. 110-139
 * The transitional zone can be regarded as the dialect boundary, where the two different dialects meet but there is no significant gap in mutual intelligibility due to the sesquilingualism of the native speakers.
 * 1) * 1978 Clyde Thogmartin, "Some 'English' Words in French," The French Review, Vol. 57, No. 4 (Mar., 1984), pp. 447-455
 * In Pilch's terminology, sesquilingualism ("mastery of one-and-a-half languages") occurs when "all members of a given society speak the inferior [sic] language, but only some of its members speak the prestige language, usually in a more or less imperfect manner as a 'foreign language.'"

Translations

 * Spanish: sesquilingüismo