The selection for the national team is updated only four times per season. A shortlist with interesting players is automatically generated. The national manager can pick 18 to 23 players from this list who can be used for international matches till the next selection is made.
The shortlists are created in week 2, 11, 23 and 42. The national manager will have 2 days to select players from the shortlist before the selection becomes final.
If there is no national manager or if the national manager doesn't respond in time, the computer will make a national selection with the best players.
The shortlist selection is made based on many criteria. Star value is only one of them. It is therefore possible that there are players on the shortlist that have a lower star value than other players from the same country that are not on the shortlist.
The goal of the shortlist is to contain the best keeper, the best 6 defenders, 5 midfielders and 3 forwards. The rest of the shortlist contains players that are either close to the best players or interesting for another reason. This may be because of special attributes, high talent or high main skill.
It's also possible that some players are selected because of the way they are trained, for example a DM and AM need different skills. The shortlist should contain several of both types.