The Indian states were first delimited linguistically in:

The states of India were first extensively delimited on a linguistic basis under the States Reorganisation Act, which was passed in 1956. This came into effect in November 1956, leading to the creation of 14 states and 6 union territories based primarily on linguistic boundaries. While Andhra State was created on a linguistic basis earlier in 1953, the comprehensive, nationwide linguistic delimitation of Indian states officially occurred in 1956.