Can you give the command you were running with the exact arguments, and also a file containing the XML entry for the page causing the problem (and the xml namespace/header lines and footer lines so that it's a complete if tiny file)?

I was importing latest it.wiki's xml pages' dump, namely itwiki-20161201-pages-meta-current.xml.bz2 (MD5 checked). I think you can more efficently look for the relevant line in dump than me, otherwise I'll try. It seems to encounter a https://chars.suikawiki.org/char/1050A char needing a fourth byte to be encoded. I've subscribed Ori since he seems to have already dealt with a similar issue in another context.

C:\Users\USERNAME\Desktop>java -classpath C:\Users\USERNAME\Desktop\mariadb-java-client-1.5.4.jar;C:\Users\USERNAME\Desktop\mwdumper.jar org.mediawiki.dumper.Dumper --output="mysql://127.0.0.1/DBNAME?user=USERNAME&password=PASSWORD" --format=sql:1.5 itwiki-20161201-pages-meta-current.xml.bz2

show variables like 'char%';

+--------------------------+---------------------------------+

+--------------------------+---------------------------------+

[...]

You actually ran across https://chars.suikawiki.org/char/1D50A as far as I see. The page in question would be https://it.wikipedia.org/wiki/Discussioni_utente:%F0%9D%94%8A then.

As a workaround, you might want to just manually remove that from the dump or change the page title.

I'm still puzzled, it seems to be a true 4byte char trying to be insert in a column whose encoding is 3byte.

I eventually managed to fix it: WMF's install actually uses VARBINARY(255) instead of VACHAR(255) (as for mediawiki's default) for page_title column. An ALTER table 'page' CHANGE COLUMN 'page_title' 'page_title' VARBINARY(255) NOT NULL COLLATE 'binary'; did the trick. I'll go on testing around and I'll eventually change mediawiki.org's mwdumper guide.