I had the same problem with French accented chars.
You need to set these properties for the font to be applied to accented characters. For instance :
RunFonts font = new RunFonts();
font.Ascii = font.HighAnsi = font.ComplexScript = @"Calibri";
So for modify your code as the following :
RunFonts font1 = new RunFonts() {
Ascii = "Gotham Narrow Medium",
HighAnsi = "Gotham Narrow Medium",
ComplexScript = "Gotham Narrow Medium" };