http://neilcummins.com/tie_cog.pdf
https://www.ips-journal.eu/index.php?id=343&L=0&tx_news_pi1%5Bnews%5D=3433&tx_news_pi1%5Bcontroller%5D=News&tx_news_pi1%5Baction%5D=detail&cHash=d423ae64c4b25e2b5dc104f032109b1e
https://www.britishcouncil.org/sites/default/files/languages_for_the_future_2017.pdf
https://home.treasury.gov/system/files/136/Treasury_Study_WoA.pdf