You can never learn too much about your native language.

Literal

Mother-tongue [about-については] how-much-ever lots learn-[even-ても] sufficient is-not

いくら~ても = 'no matter how much you...' — a concessive pattern meaning the action is never enough. 母語 (ぼご) = mother tongue/native language. ~ても here means 'even if you learn a lot, it's still not sufficient.'