And one last update. After reading the wiki and checking with my hosting provider, I have created a php.ini file for all my directories containig this:
Text Formatted Code
mbstring.language = Spanish
mbstring.func_overload = 7
mbstring.internal_encoding = UTF-8
mbstring.http_input = UTF-8
mbstring.http_output = UTF-8
mbstring.encoding_translation = On ; No difference if I turn this On or Off
I don't know much about php; however, my hosting provider insists that these php.ini settings should solve my problem.
Well, I have improved a little bit. Now the search function can find special Spanish characters in titles of static pages, but in titles only,not in the body of the static page nor anywhere else in my site.