ok thxs.
I read https://wiki.apache.org/tomcat/FAQ/CharacterEncoding but didn’t manage to fix my issue (server.xml was fine and web.xml editing without changes).
Anyways I edited some entries of xwikiattachment (add image/svg+xml and UTF-8), restart my tomcat 8.5.11 to fix my issue.
I think I will launch an sql query to fix my issue…
UPDATE xwiki.xwikiattachment
SET xwa_mimetype='image/svg+xml', xdd_charset='UTF-8'
WHERE xwa_filename like '%.svg';