Amir Khusrau

Here's something about early Indian mixed-language poetry:

"In Hindi, for instance even before the advent of the four recognized categories of Bhakti poetry Gyana-Kshri, Prem Margi Sufi, Ram Bhakti and Krishna Bhakti , the emergence of Amir Khusrau was noticeable . Though mainly a Persian poet, born in Patiali (Uttar Pradesh) or, according to some scholars, in Delhi Khusrau was a devout mystic and disciple of the Sufi saint Hazrat Nizamuddin Auslia of Delhi, and his bridal songs, riddles and stray couplets mark the beginning of poetry in a mixed language with an amalgam of Khari Boli grammatical syntax and a sprinkling of Turkish, Persian and Arabic words. He sings praises of his motherland and mixes with the common man of his times so as to give unhampered expression to his feelings with exuberance and spontaneity."

When poets write in the "real language of men" (and women), they have no choice but to mix languages, because real men and women, in most countries that are not isolated, use words from other languages to beef up their own.  No language is adequate to express everything that a human being feels; sensitive and articulate real men and women use words, ideas, and structures available from whatever language.  Poets that speak for and to real men and women (not just to literary critics or linguists or language teachers) similarly harness the resources of every language they can get a hold of.  If poetry indeed aspires to the condition of music (the universal language), then poetry has to use not just one language but as many as the poet can manage.