Both are present tense. Learning a language is a special case where you probably want to use "am learning English" if you are currently learning English. Normally, you use these two verb forms to distinguish if you are in the moment performing the action or are speaking in a general way. For example: I ride my bike to school. - This is a general comment about how I transport myself to school. I am riding my bike to school. - At this very moment, you can find me on my bike, riding to school. Notice that this is a verb that requires movement that would be difficult to perform forever. For example, I "am going" to the movies - you won't go to the movies in every moment, but in this moment you are. Certain verbs, like studying or learning, are generally used in the form "am studying" or "am learning." When you say "I am learning English" you don't have to right in that moment be actively learning English. Unlike the verb "ride," you can continue to learn forever.

You are right that present continuous (be + verb + ing) is for things you are doing right now. Examples: I'm using the computer. She's watching a movie. He's sleeping. You can also use present continuous to talk about things happening "around now." Examples: I'm exercising a lot these days. (= I often exercise; this is a recent habit) She's dating her friend's cousin. (= They often go on dates recently.) "I'm learning English" describes something that is happening "around now" -- a relatively new or recent habit. "I learn English" is OK and has basically the same meaning, but "I'm learning English" sounds more natural.

That question is very ambiguous. I am learning English means you're learning English right now. You can also say- I am currently learning English - That means In these days, you are learning English. I learn English means you learn English every day. In my humble opinion, you never stop learning a language. Yeah, it's true, people say " I am learning English, or I am currently learning whatever".

the diff. i guess is we use the Present Continuous tense to speak about things which are happening now or things which are temporary, which in your example means like if you are attending some classes or course, while the Present Simple tense describes usual, repeated and permanent things - for example, always, usually, often, sometimes, never like if your learning the language for a long open period of time , hope i made it clear and correctly, regards