$LC_ALL$LANGGetUserDefaultLocaleNameGetSystemDefaultLocaleNamegetWindowsLocale()
en_USfr_FR
lang := "ru_RU"
tag := language.MustParse(lang)

inEng := display.English.Languages()
inTur := display.Turkish.Languages()
inSelf := display.Self

fmt.Println(inEng.Name(tag))
fmt.Println(inSelf.Name(tag))
fmt.Println(inTur.Name(tag))

   // Output:
   // Russian
   // русский
   // Rusça