Complex sentence: With the process of Romanization, in the centuries of Roman Empire, they adopted Latin Language (Vulgar Latin) and roman civilization, their old language, aquitanian language, is the substrate of gascon language (a romance language) spoken by the gascons.
Split into simpler sentences: With the process of Romanization, in the centuries of Roman Empire, they got an imprint of the Latin Language (Vulgar Latin) and Roman civilization. Their old language, the Aquitanian language, is the substrate of Gascon language (a romance language) spoken later by the Gascons.