[rahimnathwani]

  If your mother tongue is Korean (e.g Korean American) that only just started learning, it only take one day turnover from illiterate to literate.

Heritage speakers (of any language, not just Korean) often have limited vocabulary and limited exposure to complex grammar. Being able to sound out words wouldn't be enough to allow a heritage speaker able to fluently read a newspaper.

How many Korean-Americans know the Korean words for things like 'legislature', 'inflation', or 'geopolitical tensions'?