Default to a UTF-8 locale in Java stub template

On non-macOS Unix, without any locale variable set, the OpenJDK defaults
to using ASCII rather than UTF-8 as the encoding for file system paths
(i.e., the value of the `sun.jnu.encoding` property).

src/main/java/com/google/devtools/build/lib/bazel/rules/java/java_stub_template.txt

@@ -362,6 +362,13 @@ if [ -z "$CLASSPATH_LIMIT" ]; then
   is_windows && CLASSPATH_LIMIT=7000 || CLASSPATH_LIMIT=120000
 fi
 
+# On non-macOS Unix, without any locale variable set, the OpenJDK defaults to
+# using ASCII rather than UTF-8 as the encoding for file system paths (i.e., the
+# value of the sun.jnu.encoding property).
+if ! is_macos && ! is_windows && [ -z "$LC_ALL" ] && [ -z "$LC_CTYPE" ] && [ -z "$LANG" ]; then
+  export LC_ALL=C.UTF-8
+fi
+
 if (("${#CLASSPATH}" > ${CLASSPATH_LIMIT})); then
   export JACOCO_IS_JAR_WRAPPED=1
   create_and_run_classpath_jar

src/test/shell/bazel/unicode_filenames_test.sh

@@ -206,4 +206,32 @@ function test_utf8_source_artifact_in_bep() {
   expect_log '"name":"pkg/srcs/ünïcödë fïlë.txt"'
 }
 
+function test_utf8_filename_in_java_test() {
+  touch WORKSPACE
+
+  mkdir pkg
+
+  cat >pkg/BUILD <<'EOF'
+java_test(
+    name = "Test",
+    srcs = ["Test.java"],
+    main_class = "Test",
+    use_testrunner = False,
+)
+EOF
+
+  cat >pkg/Test.java <<'EOF'
+import java.nio.file.Files;
+import java.io.IOException;
+
+class Test {
+    public static void main(String[] args) throws IOException {
+        Files.createTempFile("æøå", null);
+    }
+}
+EOF
+
+  bazel test //pkg:Test --test_output=errors 2>$TEST_log || fail "Test should pass"
+}
+
 run_suite "Tests for handling of Unicode filenames"