Thank you for your prompt response,
1) Atahulpa 3.7.23 and WP 4.1.1
2) The faulty url is:
http://kemalgencay.com/bir-kez-daha/
Except the beige element which displays "?" for just one Turkish character, everything works fine for the whole site.
3) When I switch to twenty-fifteen the menu does not display, so I can not display the page /bir-kez-daha/ !
Maybe it is the particular font for the element but I could not locate it despite I use firebug in Firefox.
Best regards
Kemal