How to translate the toolbar into multiple languages?

Hello dear members of LibreOffice support,

I want to translate an application based on Macros developed in French 
to include default English for our GNU/Linux distribution.

I've already found how to translate dialog boxes into multiple 
languages, and have default English: 
https://help.libreoffice.org/Basic/Translation_of_Controls_in_the_Dialog_Editor

I can not find on the Internet how to have the translation of the text 
of the icons of a toolbar in English by default, and also in French 
according to the language selected by the user.

My files for defining the toolbar are called custom_toolbar_XXXX.xml, 
and are in this format:

|<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE toolbar:toolbar PUBLIC 
"-//OpenOffice.org//DTD OfficeDocument 1.0//EN" "toolbar.dtd"> 
<toolbar:toolbar xmlns:toolbar="http://openoffice.org/2001/toolbar"; 
xmlns:xlink="http://www.w3.org/1999/xlink"; toolbar:uiname="Niveau1 
medias"> <toolbar:toolbaritem 
xlink:href="vnd.sun.star.script:Standard.Module6.gerer_cadre_image1?language=Basic&amp;location=application" 
toolbar:text="Ajouter ou modifier une image"/> <toolbar:toolbaritem 
xlink:href="vnd.sun.star.script:Standard.Module6.aggrandir_cadre_images?language=Basic&amp;location=application" 
toolbar:text="Agrandir l&apos;image"/> <toolbar:toolbarseparator/> 
<toolbar:toolbaritem 
xlink:href="vnd.sun.star.script:Standard.Module6.gerer_fond_ecran?language=Basic&amp;location=application" 
toolbar:text="Ajouter ou modifier une image de fond "/> </toolbar:toolbar> |

Is it possible to put a language attribute in these files to specify on 
which language the translation carries?

If not, where can we find the syntax of the toolbar.dtd format?

Thanks in advance for your help.

Best regards,

Patrick