Change Font Size based on Culture

I’m using a composite font set up with a default font and a sub font that supports Russian that is scaled down. When I choose the Cyrillic character range for the Russian sub font it’s working. Problem is for any characters outside that Range like Numbers or English words the default font is used without the scaling. There is this Cultures filter but when I add “ru-RU” the sub font gets ignored. I tried it with and without a character range. I also tried different culture names (ru, RU-ru, ru;ru-RU). But it’s not working. This happens also in standalone and packaged build. Unreal Engine 5.3.2.