The correct options are
B He used foreign languages in his writings.
C He weakened the idea of Bhakti.
Saint Jnaneswar was also known as Dnyaneshwar. He was a poet, and philosopher; active during the thirteenth century in Maharashtra. He used the local language so that common people could understand the underlying philosophy and teachings. He helped in strengthening the idea of Bhakti by opening the door of knowledge to the common people.