Since update to PHP 7.2 there is a problem with with decimal point in the values of a srcset for images.
expected: srcset="URL1 1.5x, URL2 2x" [.]
but you get: srcset="URL1 1,5x, URL2 2x" [,]
The image display fails. For now I disabled the Responsiv Images. But I don't know where else this problem occurs.
Locale is set to:
$wgShellLocale = "de_DE.utf8";
mediawiki 1.29 and now 1.30rc