magento i18n:pack [-m|--mode={merge|replace}] [-d|--allow-duplicates] <source> <locale>

i18n:pack [-m|--mode="..."] [-d|--allow-duplicates] source pack locale

sudo php bin/magento i18n:pack -d app/i18n/tamil/tn_tn/tn_TN.csv tn_TN tn_TN

Successfully saved tn_TN language package.