Since you are talking about a process or something that continues, you should use the Present Perfect Continuous tense. You could say, I have been learning English on my own. I have been learning English by myself. I have been learning English alone. ( This sentence is confusing because it sounds like you are learning only English) I have been learning English without any help. Hope this helps

I am learning English with no help = the most correct and least ambiguous sentence, it is saying you are learning and you are receiving no help, either, physical, or financially in the form of a grant or student loan etc. The other sentences are understandable except the third one. This could imply you are either learning (alone in a room) or (learning ONLY English) All four sentences leave you open to receiving differences of opinion from teachers, and with differences between daily colloquial speech and what tenses are taught by teachers. "I am self taught at English, with no help, from anybody/anyone, financially or otherwise" sometimes English requires the long sentences it is known for. when it does you have to use the long sentences, to be fully understood, by everybody.

You don't have to use the Present Perfect Continuous tense. It could be something you just do once and then move on to something else, but you do that thing every day, or often. For example: A) I wash the dishes. It happens daily, but I do it and then it's done until the next time. Present tense, it's something I do. It just happens. B) I have been washing the dishes. Has 2 possibilities: 1) I am still in the process of washing the dishes, and it's been taking a long time. 2) I am the one who has been making sure the dishes are (or were) being washed during a period of time (like the past week), and I am still the one making sure the dishes are being washed. Present Perfect Continuous includes part of the past and is continuing forward. (Naomi can correct me if I'm wrong, lol!) :)

a)I learn English on my own. I learn English alone. b)I learn English by myself. I learn English with no help. I think they are similar in meaning, but a) can mean that you study alone, with no other people present. b) can mean you do not receive help with your learning.

All of those phrases are correct. :)