"The dog speaks Korean, too."
Translation:개도 한국어로 말합니다.
It should be accepted. The question is emphasis, which is hard to deduce from a short English sentence without context. 개는 한국어로도 말합니다 means that the dog (as opposed the cat) speaks Korean (in addition to some other language). 개도 한국어로 말합니다 means that the dog (in addition to the cat) speaks Korean.
I think it could be. Hopefully, a native speaker will help us out. I found these at https://www.howtostudykorean.com/unit-5/lessons-101-108/lesson-107/-- 제주도가 신선한 공기로도 유명해요 = Jeju is also famous for its fresh air
그 영화가 일본어로도 번역되었다 = That movie was also translated to Japanese
요즘에는 사람들이 컴퓨터로도 통화할 수 있어요 = These days, people can also talk over (using) computers
우리가 피자를 점심으로도 먹었어요 = We also ate pizza for lunch
비상상태에서는 의자를 구명조끼로도 쓸 수 있다 = In an emergency situation, you can also use your seat as a life jacket