Shell Programming and Scripting

awk -F"[:,]" '
NR==FNR{a[$2]=$1;next;}   # (1) It only builds array a for file2 (that's the first file in awk command) , NR==FNR is used to control it. 
a[$3]  # (2) then check if we have the same value in arrary a a[$3]'s value is not 0 or null. 
{ print $1,$2,$3,a[$3]}' file2  # First file
 OFS="," file1  # second file

For the third question, I am not really understand. Do you mean you need update more files with country and city, then just add the file name one by one.

awk .....  file2 OFS="," file1 file3 file4 file5