Complex sentence: There is a significant population who identify as non-Arab in the region: this population is the Lebu (Berbers), who did not adopt Arabic language over the times and who kept their distinct Berber dialect.
Split into simpler sentences: There is a significant population who identify as non-Arab in the region. This population is the Berber-speaking Berbers, who did not adopt Arabic language over the times and who kept their distinct Berber dialect.