This is a much debated question. But here's the short of it:

• Languages cannot be copywrited nor owned
• Scripts (formation of letters and such) cannot be copywrited nor owned
• Works within a language can be copywrited and owned
• Fonts can be copywrited and owned

This means that you are free to use the language and dragon runes as you wish, but you CANNOT quote nor reproduce lines from the game, nor can you use the font from the game (yes, the use of this font without permission from big Beth is illegal). However, there is a possibility that the font may be abandonware, which is controversial in itself. You can just use a dragon rune font made from scratch, as linked in my bio or found on FontStruct.