After fixing 0002545 I tried the specified Roboto Condensed font and it works as expected, so I think your problems were related to the previous ticket.
I tested the following xaml:

<TextBlock Text="Hello World" FontFamily="pack://application:,,,/Fonts/#Roboto Condensed"/>

<TextBlock Text="Hello World" FontFamily="/Fonts/#Roboto Condensed"/>

<TextBlock Text="Hello World" FontFamily="Fonts/#Roboto Condensed"/>

And in all cases the font selected was the correct one.

Could you share the xaml you were using and the file structure (and providers) that were failing for you?

I see now what is happening, in 3.2 we fully implemented the font differentiation algorithm used by WPF (0001868).
This means that if a style is included in the FontFamily name it will try to match that, overriding the style attributes, so for example:

This text will use "Roboto" + Condensed + Italic, which is "Roboto Condesed Italic" font:

<TextBlock Text="Hello World" FontFamily="Fonts/#Roboto" FontStretch="Condensed" FontStyle="Italic"/>

<TextBlock Text="Hello World" FontFamily="Fonts/#Roboto Condensed" FontStyle="Italic"/>

<TextBlock Text="Hello World" FontFamily="Fonts/#Roboto Condensed Italic"/>

<TextBlock Text="Hello World" FontFamily="Fonts/#Roboto Condensed Italic" FontWeight="Bold"/>

<TextBlock Text="Hello World" FontFamily="Fonts/#Roboto Condensed Bold Italic"/>

Our recommedation is to use the plain family name "Roboto", and then specify the rest of styles as attributes. So you can define styles like this:

<FontFamily x:Key="RobotoFont">../Fonts/#Roboto</FontFamily>

<Style x:Key="Roboto" TargetType="TextBlock">

<Setter Property="FontFamily" Value="{StaticResource RobotoFont}"/>

<Setter Property="FontStretch" Value="Condensed"/>

</Style>

<Style x:Key="RobotoBoldItalic18" TargetType="TextBlock" BasedOn="{StaticResource Roboto}">

<Setter Property="FontSize" Value="18"/>

<Setter Property="FontStyle" Value="Italic"/>

<Setter Property="FontWeight" Value="Bold"/>

<Setter Property="LineHeight" Value="20"/>

<Setter Property="TextWrapping" Value="Wrap"/>

</Style>

Okay, I see now. Thanks for clarifying it. Yeah using Roboto as the font family name and then specifying weight, spacing etc. separately seems to work correctly. It was a little confusing, since the font is called "Roboto Condensed", which is why I was referencing it the way I originally was. But your solution seems to work fine. Thank you!