"Intensive language learning" . . "learning a foreign language" . "systematic learning" . "second-language acquisition theory" . . "easier-to-learn" . . "foreign language teaching" . . "SLA" . . "external factors" . . "second language proficiency" . "Second-language acquisition" . . "language courses" . . "learn a second language" . "second-language acquisition" . . . . "second language learning" . "Second-language education" . . . . . . . "learners" . "L2 learners" . "second language" . "Second language acquisition" . . . "second language acquisition." . "foreign language learners" . . . "Foreign language learning" . . "L2 acquisition" . . . "Second Language Acquisition" . "second language (L2) acquisition" . "foreign language acquisition" . "acquired" . . "L2" . "transfer effects" . "second language acquisition" . . "Second-language acquisition" . "second-language learning" . . . "Second-language_acquisition#Computational_models" . . . "second languages" . "learning additional languages" . "second-language learners" . . . . "Second-language acquisition#Stages" . "second language vocabulary acquisition" .