* Sursagar Rag: This is a classical Indian raga (a melodic framework) and is not associated with a specific language. Raga is a musical concept, not a linguistic one.
* Sursagar by Surdas: This is a famous devotional poetry collection in Braj Bhasha, a dialect of Hindi. It is written in the "doha" form, a popular poetic form in Hindi literature.
* Sursagar by Jayasi: This is another famous poetic work in Awadhi, a language closely related to Hindi, spoken in the Awadh region of Uttar Pradesh in India. It's a romantic epic about the legendary love story of Raja Salbahan and Padmavati.
Therefore, depending on what "Sursagar" you are referring to, the language could be Braj Bhasha or Awadhi.