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-Adobe InDesign teamSigurdur Armannsson commented
For those who come here searching for solutions for their Hunspell problems in InDesign 2016, 2017, 2018 2019 and most likely 2020 should try to install this https://font.is/hunspell-hyphenation-for-indesign-cc-2019/
It is complete solution for Icelandic but at the same time solves Hunspell for manually installed Hunspell files that do not work.