Elaborated on Haugen's 4 stage model with a 7 stage model:
Selection - Language selected is usually prestigious.
Acceptance - People have to agree with it and use it.
Diffusion - It has to spread out and become widely used.
Maintenance - People may then fix and adjust what they feel is necessary.
Elaboration of Function - Used in many different contexts.
Codification - Establishment of normal rules.
Prescription - Rules are established and followed.