FULL PRODUCT VERSION :
$ java -version
java version "9-ea"
Java(TM) SE Runtime Environment (build 9-ea+159)
Java HotSpot(TM) 64-Bit Server VM (build 9-ea+159, mixed mode)


ADDITIONAL OS VERSION INFORMATION :
Linux rhxxxx.microfocus.com 2.6.32-131.0.15.el6.x86_64 #1 SMP Tue May 10 15:42:40 EDT 2011 x86_64 x86_64 x86_64 GNU/Linux


EXTRA RELEVANT SYSTEM CONFIGURATION :
No locale to be set.

A DESCRIPTION OF THE PROBLEM :
If there is a file present in the current directory whose name consists of ShiftJIS characters, and my locale is not set, 'javac HelloWorld.java' (obviously a trivial Java program) fails.

REGRESSION. Last worked in version 8u121

ADDITIONAL REGRESSION INFORMATION:
java version "9-ea"
Java(TM) SE Runtime Environment (build 9-ea+159)
Java HotSpot(TM) 64-Bit Server VM (build 9-ea+159, mixed mode)


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
First we must create a file with a Japanese ShiftJIS name.
You need a terminal that supports Japanese ShiftJIS first. I do...

$ LANG=ja_JP.SJIS xterm&

... which creates an xterm. I cannot read or write Japanese, so I then do 'ls notexist' to get an error in Japanese from 'ls', and cut and paste some Japanese characters from that error and use 'touch' to create the file...

$ touch <pasted-Japanese-characters>

There is now a file with a name consisting on ShiftJIS Japanese characters.
In another terminal (or the Japanese one - it doesn't really matter) unset your language settings, and check your locale - it should now default to 'POSIX'

$ unset LANG
$ unset LC_ALL
$ locale
LANG=
LC_CTYPE="POSIX"
LC_NUMERIC="POSIX"
LC_TIME="POSIX"
LC_COLLATE="POSIX"
LC_MONETARY="POSIX"
LC_MESSAGES="POSIX"
LC_PAPER="POSIX"
LC_NAME="POSIX"
LC_ADDRESS="POSIX"
LC_TELEPHONE="POSIX"
LC_MEASUREMENT="POSIX"
LC_IDENTIFICATION="POSIX"
LC_ALL=

Next we'll be trying to compile 'HelloWorld.java' - here it is...

public class HelloWorld {

    public static void main(String[] args) {
        System.out.println("Hello, World");
    }

}

... now to compile it


$ javac HelloWorld.java


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
HelloWorld.java compiles without any warning or error.
ACTUAL -
$ javac HelloWorld.java
An exception has occurred in the compiler (9-ea). Please file a bug against the Java compiler via the Java bug reporting page (http://bugreport.java.com) after checking the Bug Database (http://bugs.java.com) for duplicates. Include your program and the following diagnostic in your report. Thank you.
java.nio.file.InvalidPathException: Malformed input or input contains unmappable characters: ?????????????y
at java.base/sun.nio.fs.UnixPath.encode(UnixPath.java:145)
at java.base/sun.nio.fs.UnixPath.<init>(UnixPath.java:69)
at java.base/sun.nio.fs.UnixFileSystem.getPath(UnixFileSystem.java:280)
at java.base/java.nio.file.Path.resolve(Path.java:402)
at jdk.compiler/com.sun.tools.javac.file.RelativePath.resolveAgainst(RelativePath.java:60)
at jdk.compiler/com.sun.tools.javac.file.JavacFileManager$DirectoryContainer.list(JavacFileManager.java:478)
at jdk.compiler/com.sun.tools.javac.file.JavacFileManager.list(JavacFileManager.java:713)
at jdk.compiler/com.sun.tools.javac.code.ClassFinder.list(ClassFinder.java:722)
at jdk.compiler/com.sun.tools.javac.code.ClassFinder.scanUserPaths(ClassFinder.java:648)
at jdk.compiler/com.sun.tools.javac.code.ClassFinder.fillIn(ClassFinder.java:529)
at jdk.compiler/com.sun.tools.javac.code.ClassFinder.complete(ClassFinder.java:293)
at jdk.compiler/com.sun.tools.javac.code.Symtab.lambda$addRootPackageFor$7(Symtab.java:758)
at jdk.compiler/com.sun.tools.javac.code.Symbol.complete(Symbol.java:633)
at jdk.compiler/com.sun.tools.javac.comp.Enter.visitTopLevel(Enter.java:354)
at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCCompilationUnit.accept(JCTree.java:529)
at jdk.compiler/com.sun.tools.javac.comp.Enter.classEnter(Enter.java:285)
at jdk.compiler/com.sun.tools.javac.comp.Enter.classEnter(Enter.java:300)
at jdk.compiler/com.sun.tools.javac.comp.Enter.complete(Enter.java:570)
at jdk.compiler/com.sun.tools.javac.comp.Enter.main(Enter.java:554)
at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.enterTrees(JavaCompiler.java:1073)
at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:944)
at jdk.compiler/com.sun.tools.javac.main.Main.compile(Main.java:302)
at jdk.compiler/com.sun.tools.javac.main.Main.compile(Main.java:162)
at jdk.compiler/com.sun.tools.javac.Main.compile(Main.java:55)
at jdk.compiler/com.sun.tools.javac.Main.main(Main.java:41)


ERROR MESSAGES/STACK TRACES THAT OCCUR :
$ javac HelloWorld.java
An exception has occurred in the compiler (9-ea). Please file a bug against the Java compiler via the Java bug reporting page (http://bugreport.java.com) after checking the Bug Database (http://bugs.java.com) for duplicates. Include your program and the following diagnostic in your report. Thank you.
java.nio.file.InvalidPathException: Malformed input or input contains unmappable characters: ?????????????y
at java.base/sun.nio.fs.UnixPath.encode(UnixPath.java:145)
at java.base/sun.nio.fs.UnixPath.<init>(UnixPath.java:69)
at java.base/sun.nio.fs.UnixFileSystem.getPath(UnixFileSystem.java:280)
at java.base/java.nio.file.Path.resolve(Path.java:402)
at jdk.compiler/com.sun.tools.javac.file.RelativePath.resolveAgainst(RelativePath.java:60)
at jdk.compiler/com.sun.tools.javac.file.JavacFileManager$DirectoryContainer.list(JavacFileManager.java:478)
at jdk.compiler/com.sun.tools.javac.file.JavacFileManager.list(JavacFileManager.java:713)
at jdk.compiler/com.sun.tools.javac.code.ClassFinder.list(ClassFinder.java:722)
at jdk.compiler/com.sun.tools.javac.code.ClassFinder.scanUserPaths(ClassFinder.java:648)
at jdk.compiler/com.sun.tools.javac.code.ClassFinder.fillIn(ClassFinder.java:529)
at jdk.compiler/com.sun.tools.javac.code.ClassFinder.complete(ClassFinder.java:293)
at jdk.compiler/com.sun.tools.javac.code.Symtab.lambda$addRootPackageFor$7(Symtab.java:758)
at jdk.compiler/com.sun.tools.javac.code.Symbol.complete(Symbol.java:633)
at jdk.compiler/com.sun.tools.javac.comp.Enter.visitTopLevel(Enter.java:354)
at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCCompilationUnit.accept(JCTree.java:529)
at jdk.compiler/com.sun.tools.javac.comp.Enter.classEnter(Enter.java:285)
at jdk.compiler/com.sun.tools.javac.comp.Enter.classEnter(Enter.java:300)
at jdk.compiler/com.sun.tools.javac.comp.Enter.complete(Enter.java:570)
at jdk.compiler/com.sun.tools.javac.comp.Enter.main(Enter.java:554)
at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.enterTrees(JavaCompiler.java:1073)
at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:944)
at jdk.compiler/com.sun.tools.javac.main.Main.compile(Main.java:302)
at jdk.compiler/com.sun.tools.javac.main.Main.compile(Main.java:162)
at jdk.compiler/com.sun.tools.javac.Main.compile(Main.java:55)
at jdk.compiler/com.sun.tools.javac.Main.main(Main.java:41)
$


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
public class HelloWorld {

    public static void main(String[] args) {
        System.out.println("Hello, World");
    }

}


---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
If the locale is 'en_GB.UTF8' the compilation works.... and, yep ja_JP.utf8 also. C does not.

$ export LANG=en_GB.UTF8
$ javac HelloWorld.java