LibreOffice - Setting UI Language

http://help.libreoffice.org/Common/Selecting_the_Document_Language

Setting UI Language A standard installation of LibreOffice software will give you a user interface (UI) of your chosen language.

Most users download the American English version, which gives you English menu commands and English application help. If you want another language for the menus (and for the application help, if available in that language), change the UI language as follows.

• Choose LibreOffice - PreferencesTools - Options - Language Settings - Languages.
• Select another UI language in the "User interface" listbox.
• Click OK and restart the LibreOffice software.
• If the listbox doesn't list the language that you want, see "Adding More UI Languages".

(Herramientas/Opciones/Configuración de idioma/Idiomas -> Interfaz del usuario)