Strong arguments 

To summarise, it is spelled as Kyiv in English language because:
 1) Ukrainian government insists on Kyiv spelling
 2) The State Department of the U.S. issued a directive to write Kyiv
 3) The Prime Minister of the U.K. calls the city Kyiv
 4) United Nations Multilingual Terminology Database (the ultimate body on geographical names) approved it as Kyiv
 5) Major English speaking governments worldwide switched to Kyiv spelling
 6) CIA refers to the city as Kyiv
 7) The name of the famous football club is Dynamo Kyiv
 8) Many papers, e.g., British The Guardian, are already writing Kyiv
 9) All major Canadian media already use the spelling of Kyiv
 10) and many more reasons http://kyiv.of-cour.se/
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