Opciones > Preferencias > Subtítulos [Propiedades de Subtítulos]
Click on [Fuente]
Опции > Настройки > Субтитры [Настройки субтитров]
Click on [Шрифт]
Now select a standard
font like e.g. Ariel or Verdana or Times New Roman
(Do not select "Symbol"-font! Leave
Script on "Western European".)
Do other applications (like e.g. notepad/wordpad or any wordprocessor) properly show Spanish texts? 
(You may have to do this separately for [Primary subtitles] and [Secondary subtitles].)