Sandhya Bhasa is a hard-to-decipher, early form of the Bangla language. Mahamahopadhyaya haraprasad shastri discovered an old manuscript containing the oldest specimen of bangla language and literature at the royal court of Nepal in 1907. He edited the manuscript and published it as Hajar Bachharer Purana Bangala Bhasay Bauddha Gan O Doha (A Thousand-Year-Old Buddhist Songs and Distiches in Bangla, 1916). These are religious poems and called Charyashcharyavinishchaya (The Do's and Don'ts of Religious Rites). Since these were composed in verse, they were known as charyapada or Charyagiti. The dohas, or couplets, are written in abahattha.
The distiches describe the ways of mystic indoctrination into the sahajiya cult. The writers use figurative and symbolic language to communicate their esoteric ideas. This is why Haraprasad Shastri called the language 'Sandhya Bhasha' (sandhya is the Bangla word for 'dusk'). The name is appropriate on two counts: First, Bangla was gradually emerging from prakrit and apbhrangsha -Abahattha, but some characteristics of the early languages were still present in Bangla. Secondly, because of the use of symbolic codes, the statements are sometimes explicit and sometimes implicit, resembling the state at dusk when things are partially visible.
The following example from the Charyapada shows the poet's use of metaphors and similes to express mystic ideas.
Nana taruvara maulilare ganata lageli dali
Ekeli savari evana higui karnakundula vajradhari \ dhru\
Tia dhaukhat padila savaro mahasuhe seji chhaili
Savaro bhujabga nairamani dari pehma rati pohaili \ dhru\
Translation: Various trees were in flower, and their branches touched the sky. The huntress, adorned with earrings and lightning, roams the jungle. The huntsman laid out the cot made of three elements and prepared the bed; and he passed the night with his lover. [Mohammad Daniul Huq]