I've updated Geany to 1.38 (geany-1.38_osx-2.dmg) and found that it no longer sees the dictionaries. In debug messages I found that Enchant is now 2.2.15 (was 1.x in Geany 1.37), so, as README suggests, I moved the dictionaries to the "hunspell" subdirectory while leaving the same path in the configuration dialog (parent directory of "hunspell"). Unfortunately, this didn't help, and the plugin still gives error "The Enchant library couldn't be initialized (unknown error (maybe the chosen language is not available))".