What does the "Dual Iceberg" Hypothesis suggest about languages L1 and L2?

The "Dual Iceberg" Hypothesis posits that while languages L1 (first language) and L2 (second language) may appear distinct on the surface, they share a common underlying proficiency that connects the two. This concept illustrates that both languages operate under a similar foundation of cognitive and linguistic skills, comprised of elements such as grammar, vocabulary, and discourse comprehension.

Learners utilize this underlying proficiency to transfer knowledge and skills from their first language to their second language, facilitating the development of L2. This transfer can support the learning process, as students leverage their existing language abilities to grasp new concepts in their second language. Thus, the hypothesis emphasizes the connection between L1 and L2, asserting that developing proficiency in one language can positively influence proficiency in the other, even if they are used in different contexts.