Ran a few tests in my current game with Diplomatic League & Amani.
With Diplomatic League Active:
Case 1
If Amani is the first envoy you send, you do not receive an extra envoy. Working as expected, for balance reasons.
Case 2
If Amani is present and you would otherwise have 0 envoys, assigning an envoy will only give you one envoy. Not working as expected.
Case 3
If Amani was moved, and you are reduced back to 0 envoys, assigning an envoy will give you an extra envoy. Working as expected.
In the 2nd case, I would expect to get the extra envoy. The work around of course is case 3: Moving Amani, assigning envoy, and moving Amani back.
With Diplomatic League Active:
Case 1
If Amani is the first envoy you send, you do not receive an extra envoy. Working as expected, for balance reasons.
Case 2
If Amani is present and you would otherwise have 0 envoys, assigning an envoy will only give you one envoy. Not working as expected.
Case 3
If Amani was moved, and you are reduced back to 0 envoys, assigning an envoy will give you an extra envoy. Working as expected.
In the 2nd case, I would expect to get the extra envoy. The work around of course is case 3: Moving Amani, assigning envoy, and moving Amani back.