When I read the following declaration, I'm about to think that the liste of languages for newsletter is french or enlgish only.....
I think that this list should depend on the current site possible languages... or at least use the languages usable in the admin configuration (spanish...)
<action class="org.ametys.newsletter.ribbon.CategoryWithTemplateActionButton">
<param name="action">org.ametys.newsletter.AddNewsletterAction</param>
<param name="type">newsletter-category</param>
<param name="mode">read|write</param>
<param name="label" i18n="true">PLUGINS_NEWSLETTER_CONTENT_CREATENEWSLETTERACTION_LABEL</param>
<param name="default-description" i18n="true">PLUGINS_NEWSLETTER_CONTENT_CREATENEWSLETTERACTION_DESCRIPTION</param>
<param name="disabled-description" i18n="true">PLUGINS_NEWSLETTER_CONTENT_CREATENEWSLETTERACTION_DISABLED</param>
<param name="no-template-description" i18n="true">PLUGINS_NEWSLETTER_CONTENT_CREATENEWSLETTERACTION_NOTEMPLATE</param>
<param name="icon-small" file="true">img/newsletter_16.png</param>
<param name="icon-medium" file="true">img/newsletter_32.png</param>
<param name="icon-large" file="true">img/newsletter_48.png</param>
<param name="workflowInitActionId">1</param>
<param name="workflow-workflowName">newsletter</param>
<param name="content-type-to-create">org.ametys.plugins.newsletter.Content.newsletter</param>
<param name="content-language-size">2</param>
<param name="content-language-0">fr</param>
<param name="content-language-0-label">Français</param>
<param name="content-language-1">en</param>
<param name="content-language-1-label">Anglais</param>
</action>