Java, IllegalFormatConversionException when importing an SSL certificate

Today I faced a strange problem. I needed to import an SSL certificate in a java keystore, using the “classic” keytool command. I was sure that the format of the certificate was correct, but I always received the following error:

java.util.IllegalFormatConversionException: d != java.lang.String


The reason of the error is that – in the latest versions of java – by default the keytool command uses the language of the system (in my case italian).

I had to add the parameter -J-Duser.language=en to the keytool command to made it work correctly: