Matelko wrote :
Tegimus wrote :
... You will be allowed to choose a Nationality for your Youth Academy. One of the youth players generated every season will be of this selected Nationality, and the nationality of the rest of the generated youths will be random. ...

Two youths from different countries were available in the academy this season. When I changed "Random Nationality" option to "Slovakia" in the preferred nationality settings the flags of both players changed.
But neither had a Slovak flag, one new flag of Slovenia appeared. The Slovenian flag may be a little bug (Slovakia and Slovenia are frequently confused) or it's just a coincidence and I can expect player from Slovakia only next season after preferred nation is always set.
How does it work for you?

The preferred nationality has to be set before the player is generated. If you have changed it this season, then one of the youths generated will be from the selected nationality next season.