Unfortuanly this language support file will only work for version 2 of the ad mod that only works on 1.1 rc2/rc3.
However, to get this to work, translate these strings and put them in this file Modifications.spanish.php (where spanish is either spanish or spanish_es)
$txt['js_ads_title'] = 'Ad Management';
$txt['js_text_displayads_index'] = 'Display ads on every page (ontop)';
$txt['js_text_displayads_botindex'] = 'Display ads on every page (onbottom)';
$txt['js_text_displayads_board_index'] = 'Display ads on Board Index';
$txt['js_text_displayads_display'] = 'Display ads on Thread';
$txt['js_text_displayads_message_index'] = 'Display ads on Thread Index';
$txt['js_text_displayads_firstpost'] = 'Display ads after first post';
$txt['js_text_disc'] = 'Write your code here';
$txt['js_text_help'] = 'Make sure that your code is compatible with HTML';
$txt['permissiongroup_ad_manage'] = 'Ad Management';
$txt['permissionname_ad_manageperm'] = 'Enable ads';
$txt['permissionhelp_ad_manageperm'] = 'To enable ads to appear for this membergroup, this must be checked';