Hi,
I tried everything. First I installed just ttf fonts and compile the
file but the italic Th appears in upright shape. Then I installed just
otf fonts and used
\setmainfont{Linux Libertine}
and
\setmainfont{Linux Libertine O}
separately. In the first case the result was as before but in the
later case I got \"A instead of the italic shape of "Th".