Which language learning platform's advertising slogan directly references a linguistic concept that describes the gradual process of language acquisition?

In the world of language and linguistics, advertising slogans represent a fascinating intersection of psychology, cultural linguistics, and brand strategy. The most effective slogans leverage linguistic principles to create memorable, persuasive phrases that resonate across cultures and languages. This trivia question explores how major language learning platforms have used linguistic principles in their own brand messaging to connect with their audience.

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Duolingo: "Learn a language for free. Forever."
Babbel: "Speak a new language with confidence."
Rosetta Stone: "Language Learning, Naturally."
Memrise: "Learn language the way locals speak."