Traduction Française par Serge Billon: Lire
If you’re a Joomla user who has connected his sites to Google Webmaster, you might have received the following message from the Google Search Console: “Google can’t access CSS and JS files”.
A while ago, Google announced that whether a website is mobile friendly or not is a factor in ranking websites. This message seems to be a result – Google is actively scanning websites using Webmaster and testing if they’re mobile friendly.
Since you’re blocking files Google wants to access, it could make the big G think that your site is, in fact, not mobile friendly. To avoid this, you need to tweak your robots.txt file. This is a file in your root folder which determins which robots – like Google’s bots that scan your site – can and can’t visit which folders.
To resolve this problem, you need to remove two lines from the robots.txt file; the line which disallows /media/ and /templates/. Doing this will grant Google access to the files it needs to analyze your website.
Had to do also modules, and because of JCH also plugins
french translation there : http://web54.fr/astuces/resoudre-lerreur-acces-de-googlebot-aux-fichiers-css-et-js-impossible
thanks