nbourgeo

If you want your website to be displayed only in Spanish, the simplest solution is to rename the file SMCF-es_ES.mo in smcf.mo

Your website is it only in Spanish or multilingual?

Your website is it online?

Could you confirm the value of WPLANG in wp-config.php ?
It should be es_ES

define ('WPLANG', 'es_ES');

To resolve this problem, you must change line 37 of /wp-content/pluginssimplemodal-contact-form-smcf/smcf.php :

load_plugin_textdomain("smcf", false, SMCF_DIR . "/lang/");

it become :

load_plugin_textdomain('smcf', false, dirname( plugin_basename(__FILE__) ) . '/lang');

Good luck.