Enable translation of OnlyOffice application

[js-ddev]

Whatever the chosen language in XWiki all aspects of OnlyOffice in XWiki are in english: OO interface, XWiki Administration page, and OO buttons in XWiki attachment tab.
If I looked correctly, it seems the possibility of changing the language in OnlyOffice integrated in XWiki is not available.
In the OO window, neither the settings nor the advanced settings buttons open the "Customization" page as indicated in the OO website:

• https://helpcenter.onlyoffice.com/tipstricks/portal-language.aspx
• http://www.onlyoffice.com/blog/2017/12/onlyoffice-guide-to-the-languages-and-translation-faq-and-current-achievements/