You can combine these two approaches, so something like:
I18n.translations[I18n.currentLocale()].js.composer.reply = I18n.t(themePrefix("my_translation_key"));
You can combine these two approaches, so something like:
I18n.translations[I18n.currentLocale()].js.composer.reply = I18n.t(themePrefix("my_translation_key"));