FULL PRODUCT VERSION :
java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Linux REDACTED 2.6.32-431.23.3.el6.x86_64 #1 SMP Thu Jul 31 17:20:51 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

A DESCRIPTION OF THE PROBLEM :
java.util.Locale#lookup throws a StringIndexOutOfBoundsException for some valid LanguageRanges, specifically LanguageRanges where the range has a "-" that isn't the 3rd character. An example LanguageRange that causes this is "i-navajo"

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
import java.util.Collections;
import java.util.List;
import java.util.Locale;
import java.util.Locale.LanguageRange;

List<LanguageRange> ranges = Locale.LanguageRange.parse("nv");
// the next line with throw a StringIndexOutOfBoundsException
Locale.lookup(ranges, Collections.singleton(Locale.ENGLISH));

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
A List or null. No exception should be thrown.
ACTUAL -
An exception was thrown. The stack trace:

java.lang.StringIndexOutOfBoundsException: String index out of range: -1
at java.lang.String.substring(String.java:1954)
at sun.util.locale.LocaleMatcher.lookupTag(LocaleMatcher.java:233)
at sun.util.locale.LocaleMatcher.lookup(LocaleMatcher.java:193)
at java.util.Locale.lookup(Locale.java:3261)

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.util.Collections;
import java.util.List;
import java.util.Locale;
import java.util.Locale.LanguageRange;

List<LanguageRange> ranges = Locale.LanguageRange.parse("nv");
// the next line with throw a StringIndexOutOfBoundsException
Locale.lookup(ranges, Collections.singleton(Locale.ENGLISH));
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
The workaround is to avoid passing some LanguageRanges to Locale.lookup. They can be filtered as follows:

List<LanguageRange> ranges = Locale.LanguageRange.parse("nv").stream()
  .filter(lr -> {
    int prefixIndex = lr.getRange().indexOf('-');
    return prefixIndex == -1 || prefixIndex == 2;
  })
  .collect(Collectors.toList());