You could convert \n to programmatically.
string text = "This is a line.\nThis is another line.";
IList lines = text.Split(new string[] { @"\n" }, StringSplitOptions.None);
TextBlock tb = new TextBlock();
foreach (string line in lines)
{
tb.Inlines.Add(line);
tb.Inlines.Add(new LineBreak());
}