Telerik UI For WPF R2 2019 SP1 (version 2019.2.618) Retail
Since R2 2019 SP1 (version 2019.2.618) RadFontDropDownList supports adding custom fonts (fonts that are not currently installed on the local machine). The bellow example shows how you can add the custom font.
Telerik UI for WPF R2 2019 SP1 (version 2019.2.618) Retail