Hi Marius,
Thanks for the update.
We have validated your query and you can get the specified font file string and font icon by using this link
https://andreinitescu.github.io/IconFont2Code/ and upload your UIFontIcons.ttf to view the icons.
In case of using the font icon text in XAML:
Replace
"\u" with "&#x" and add a semi colon at the end e.g.
Facebook: \ue70f =  in your code.
C#:
Need to set like
“\ue70f”
Please let us know, if you have any other concerns.
Regards,
Ruba Shanmugam