Union Government
(1) Business in Parliament shall be transacted in Hindi or English, though the presiding officer may permit a member who cannot adequately express themselves in either to address the House in their mother tongue. (2) Unless Parliament provides otherwise by law, this continues indefinitely (an original 15-year sunset on English usage was never actually allowed to take effect).
Officially, Parliament conducts business in Hindi or English, though MPs who struggle in both can get special permission to speak in their own mother tongue. In practice, both Hindi and English continue to be used indefinitely, since Parliament exercised its power to prevent the originally-planned phase-out of English.
This is why, in practice, you'll hear Parliament debates conducted in both Hindi and English (plus other Indian languages with special permission), rather than the Constitution's original 15-year plan to phase down to Hindi and regional languages only - Parliament used its own law-making power under this article to keep English in permanent use.