JDK-8171319 introduced the following code:

    private String withWeak(PublicKey key) {
        if (DISABLED_CHECK.permits(SIG_PRIMITIVE_SET, key)) {
            return String.format(rb.getString("key.bit"),
                    KeyUtil.getKeySize(key), key.getAlgorithm());
        } else {
            return String.format(rb.getString("key.bit.weak"),
                    KeyUtil.getKeySize(key), key.getAlgorithm());
        }
    }

That is the format is determined by rb.getString("key.bit.weak") or rb.getString("key.bit"). For example for -Duser.language=en, these formats are:

 %d-bit %s key

and

 %d-bit %s key (weak)

Thus, in English this expects an integer as first argument and a String as the second. In some languages however, the formats returned by rb.getString("key.bit.weak") and rb.getString("key.bit") return different format strings: E.g. String and then Integer in French or Spanish.

Attached is a simple reproducer. It fails with -Duser.language=es with:

$ javac TestKeyTool
$ java -Duser.language=es TestKeyTool
DEBUG: Format is: Clave %s de %d bits (débil)
Exception in thread "main" java.util.IllegalFormatConversionException: d != java.lang.String
at java.util.Formatter$FormatSpecifier.failConversion(Formatter.java:4302)
at java.util.Formatter$FormatSpecifier.printInteger(Formatter.java:2793)
at java.util.Formatter$FormatSpecifier.print(Formatter.java:2747)
at java.util.Formatter.format(Formatter.java:2520)
at java.util.Formatter.format(Formatter.java:2455)
at java.lang.String.format(String.java:2940)
at TestKeyTool.main(TestKeyTool.java:11)

Expected:
Ordering of format is the same as in English: Integer then String. For example in English the reproducer prints:

$ java -Duser.language=en TestKeyTool
DEBUG: Format is: %d-bit %s key (weak)
23-bit foo key (weak)
DEBUG: Format is: %d-bit %s key
23-bit foo key