When I select locale=English, the dropbox menu options at right is showed in spanish and when I select locale=Spanish the dropbox menu options at right is showed in English. The action button is translated correctly but its options are not translate correctly.
Attached an image

I am using nuxeo 5.6 and certainly, you do not have translation for spanish. In my plugin I did this translation and in my messages.properties file I added those lines:
label.userPreferences.updateLocale=Edit Locale Settings
label.userPreferences.resetTimeZone=Reset time zone from
and in my messages_es.properties file, I added thoses lines:
label.userPreferences.updateLocale=Editar la configuración regional
label.userPreferences.resetTimeZone=Cambiar zona horaria
Deploy fragment:
<?xml version="1.0"?>
<fragment version="1">
<require>org.nuxeo.ecm.webapp.core</require>
<require>org.nuxeo.ecm.platform.lang</require>
<install>
<unzip from="${bundle.fileName}" to="/" prefix="web">
<include>web/nuxeo.war/**</include>
</unzip>
<delete path="${bundle.fileName}.tmp" />
<mkdir path="${bundle.fileName}.tmp" />
<unzip from="${bundle.fileName}" to="${bundle.fileName}.tmp" />
<append from="${bundle.fileName}.tmp/OSGI-INF/l10n/messages_es.properties"
to="nuxeo.war/WEB-INF/classes/messages_en.properties" addNewLine="true" />
<append from="${bundle.fileName}.tmp/OSGI-INF/l10n/messages_fr.properties"
to="nuxeo.war/WEB-INF/classes/messages_fr.properties" addNewLine="true" />
<append from="${bundle.fileName}.tmp/OSGI-INF/l10n/messages.properties"
to="nuxeo.war/WEB-INF/classes/messages.properties" addNewLine="true" />
<delete path="${bundle.fileName}.tmp" />
</install>
</fragment>
another question is: where can I translate this section in the view user_preferences.xhtml?
Locale settings Español
Time Zone Etc/UTC - Hora Universal Coordinada