The following is Lee’s crudely approximated financial impacts (income per capita) of SESF on the cities of South Korea over the next 50 years.
Conclusion: the overall financial, cumulative impacts of speaking English over the next half a century in South Korea individually ~ $1.5-2.5 Million USD per person (averaging around $2 Million USD).
The upper bound
Cumulative impacts ~ 2 Million USD
The lower bound
Cumulative impacts for the next half a century