Hawaiian … Banned?
The short answer is no … history and the law are clear; there never was any law that banned the Hawaiian language or that made speaking Hawaiian illegal. However, many families, as a personal family decision, reportedly did not let their children speak Hawaiian. Likewise, for a period of time, Hawaiian was not the language for instruction in schools (however, schools could ask the DOE to include Hawaiian (or foreign languages) in their instruction.)
Evidence of ongoing Hawaiian language is noted by Bishop Museum, “Dozens of newspapers were published in Hawaiian between 1834 and 1949 and were read by an avid and highly literate public.” Missionaries are often blamed for discouraging use of the Hawaiian language (some even suggest they were the ones that banned its use.) That, too, is simply not correct. (Actually, the missionary efforts to establish a consistent alphabet helped save the Hawaiian language, not eliminate it.)