The Share Page email templates are inconsistent between languages

The "Share page by email" mail templates (XWiki.SharePage, one XWiki.Mail object per language) have drifted apart: some fixes were applied to the English version only, and the German version was never aligned with the others.

Problems

• French and German: the "add this document to your WatchList" link is still shown when the Watchlist is disabled (XWIKI-15043 was only applied to the English template).
• English HTML mail: the footer reads "generated by XWiki at <request server name> on behalf of <server name>" instead of "at <server name> on behalf of <user>", unlike the English plain-text mail and all the other languages. It also still uses the request server name, which can be 127.0.0.1 behind a proxy (see XWIKI-16006).
• German:
  • every line of the plain-text mail is indented with two tabs, and the shared message is indented inside the HTML mail too;
  • the HTML mail doesn't compute the server name from the wiki home page URL as the other languages do (XWIKI-16006), and the intro sentence doesn't say on which wiki the document is;
  • uses the deprecated $context binding instead of $xcontext;
  • some grammar mistakes ("Dies Nachricht ist generiert worden", "in Ihren Browser", "in die Abonnementsliste hinzufügen").
• French: small grammar mistakes ("à votre favoris", "Pour faire ça").

Expected

All languages render the same information with the same Velocity logic, only the text being translated.