I am seeking evidence that formal language planning works. Classical instances might be Hebrew and Afrikaans. I would be most grateful for research papers which provide solid evidence of the effective impact of language planning on language ecologies. I am interested in large-scale political interventions rather than changes within micro-environments. The nature and quality of the evidence supporting claims of language-planning efficacy is obviously crucial.
Language plans abound, but I would be most grateful to be pointed in the direction of data which shows that these plans have worked as intended.