While 아직 is rather neutral still/yet, 아직까지도 contains nuance of surprise and dissatisfaction, thus largely a blaming/accusing expression. 아직 기초 한국어를 공부하고 있어요: I'm still learning basic Korean (which is normal since it hasn't been for long anyway) 아직까지도 기초 한국어를 공부하고 있어요: I'm still stuck with learning basic Korean (That I'm ashamed of)

I don't think the difference is so significant, but here it is. 1. 아직 - "yet". Sounds casual, like speaking of something freshly brought up. Used more in negative phrases. 2. 아직까지 - "till now; up to this point". Used for something that has been happening or anticipated for a while. But the difference is not that important, and many people seem to use them interchangeably. You can also add 도 to both words to strengthen the meaning. Some example: A: 너 숙제 다 했니? = Have you done your homework? B: 아니요, 아직 안 했어요. = No, not yet. A: 아까부터 한다더니 아직도[아직까지(도)] 안했어? = After saying you would so many times, you still haven't? A: 축구 시합 끝났어? = Is the soccer game over? B: 아니, 아직까지 [아직도] 해. = No, it's still going on. - 아직 한국어를 공부해요 / 공부하고 있어요 = I am still studying Korean. - 아직까지도 한국어를 공부해요 / 공부하고 있어요 = (in effect) I still haven't given up on studying Korean. I don't think using 아직 in your example is wrong or strange. It just sounds more casual and light.