Language Planning can best be understood in terms of the following questions: Who plans what for whom and how?
Language planning is defined as the deliberate effort or attempt by governing agencies to manipulate the acquisition, structure or function of language codes. There are three categories of language planning, those being: status planning, which may focus on standardization as presently in Denmark; corpus planning, which is language-internal and may be illustrated by dictionaries, new vocabulary, and prescribed grammar; acquisition planning, which may typically create opportunities to acquire or improve varieties as in education, literary and literature, targeting first- and second-language acquisition differently.
According to linguists, the four primary ideological goals of language planning are linguistic assimilation, as in the U.S. English-only movement; linguistic pluralism, as in South Africa; vernacularization, as with newly standardized or written languages like Tok Pisin; and internationalization, as in a non-local variety being adopted for education etc. like in India and Taiwan. There are also other goals such as language purification, lexical development or stylistic simplification, and minority language maintenance.
Therefore, the answers to "Who plans what for whom and how?" are: Government or other official agencies or institutions plan language structure, acquisition and function for local and national speakers for various purposes through various means, such as acquisition through education.
[For more detail, see Notes for LG102, Intro Sociolinguistics, University of Essex, Prof. Peter L. Patrick, from which this Answer was drawn.]