This is incorrect English. I am teaching the subject of English makes some sense. I am teaching English is what would actually be said.
In English, this sentence requires an article, either a or the depending on context
"I am teaching an English subject!" Are you sure your qualified to teach English?
"I am teaching an English subject" is awkward, and and "I am teaching an English" is just incorrect. "I am teaching English" is correct. Reported.
To add to the comments above, in English a common question to a teacher might be: "What subject do you teach?" But in answering, the teacher typically will not use the word "subject". She/he will say "I teach reading" or "I teach French and Latin." That is why I suggest that a good translation for the above is simply: "I teach English.
eeeehhhh not really, sometimes somo is used for both, but kipindi is a more definite and proper translation meaning lesson.