True. It would probably have to be a response to a compliment or very specific statement statement. When I met my Korean exchange partner, naturally I said "안녕하세요." And he told me" Wow you speak Korean so well." I could have used this sentance then. Lol. Instead of just saying "Thats about all I know." Hahaha
As the reference point here is the other interlocutor (i.e. close in sight), probably 그만큼 would be more appropriate.
그만큼 한국어를 못해요 = I don't speak Korean as much as that.
If the reference point is known to both interlocutors but not in sight, use 그만큼 also.
Use 저만큼 (as much as that) when the reference point is far away from both interlocutors, but still in sight.
Apparently, 저 cannot be used to refer to abstract concepts / invisible points of reference.
• 하다 = to do => 합니다 = does/do (formal, polite style)
• 하다 can be used sometimes as an abbreviated form of the -하다 verbs associated with communication ( 말하다, say/speak; 이야기하다, talk; 대화하다, converse; 질문하다, ask; etc. ). But avoid using this abbreviated form in 하고 direct quotation sentences.
녹색 부엉이는 "축하합니다"하고 했습니다 (❌) = The green owl said, "Congratulations."
녹색 부엉이는 "축하합니다"하고 말했습니다 (✔) = The green owl said, "Congratulations."
• 가다 = to go => 갑니다 = go/goes (formal, polite style)