so the problem with the colon is that it has no special meaning so your regex is looking to match :/ literally – that would work for a string with a structure like:
/madagascar/subpage:/2
you would get a full match and 4 groups:
array
(
[0] => 'madagascar/subpage:/2'
[1] => 'madagascar'
[2] => 'subpage'
[3] => ':/2'
[4] => '2'
)
but since the colon is not in your tested string, all you get is a full match and two groups (only parts (madagascar|uganda)and (.?.+?)? tested positive)
array
(
[0] => 'madagascar/subpage/2'
[1] => 'madagascar'
[2] => 'subpage/2'
)