I think that Diksha and Pravartan both mean something like initiation or commencement.
Diksha apparently means "preparation" and "initiation" (and may be used ceremonially).
Pravartan is used in the Sanskrit name of the Dharmacakrapravartana Sūtra which is translated as "The Setting in Motion of the Wheel of the Dharma".
How the words are used might vary depending on the school.
I think the phrase is used in the Dalit Buddhist movement:
Twenty-two vows of Ambedkar
After receiving ordination, Ambedkar gave dhamma diksha to his followers. The ceremony included 22 vows given to all new converts after Three Jewels and Five Precepts. On 14 October 1956 at Nagpur, Ambedkar performed another mass religious conversion ceremony at Chandrapur.
He prescribed 22 vows to his followers:
- I shall have no faith in Brahma, Vishnu and Maheshwara, nor shall I worship them.
The "Three Jewels" (also called "Refuge") and the "Five Precepts", which are mentioned in the quote above, are the traditional Buddhist initiation ceremonies -- taking refuge (and various numbers of precepts) are common to all schools of Buddhism, and are one of the definitions of "being a Buddhist".