They are certainly related. Language Management Theory (LMT) is concerned with the factors that evoke change in language use. More specifically, it tends to specify those factors which accelerate language shift and those which block it and favor its maintenance under macro-level societal pressures. Differently stated, according to LMT, language shift and/or maintenance is a social practice triggered by sociocultural/ socioeconomic factors which ultimately lead either to removal/ replacement of an individual's L1 or to its maintenance.
Language management is related to language maintenance since the former may be used to ensure the the latter is achieved. Language may be managed to foster its maintenance. Language users may be restricted to using it to ensure that it is pitied against other languages and in so doing language shift is contained and attrition curbed.
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