Takes any vector of languages and returns countries where those languages are used as ISO 3166-1 alpha-2 codes.
Examples
country.lang('Korean')
#> Korean
#> "China;South Korea;North Korea;Russia"
country.lang(c('Korean', 'Polish'))
#> Korean
#> "China;South Korea;North Korea;Russia"
#> Polish
#> "Belarus;Czech;Germany;Lithuania;Poland;Russia"