this tuple should be 1-1 representation on front-end. If we will support language and country, than on front-end will be huge list with 16 en-country variants among other languages/country pairs. I think it is UX/PO question.
For example:
en-TT	English - Trinidad and Tobago	
en-GB	English - United Kingdom	
en-US	English - United States	

@nedbat @Lyla-Fischer what is the right way to have language dropdown list on front-end:
Elements:
English - Trinidad and Tobago	
English - United Kingdom	
English - United States	
or just single English?