[JENKINS-73246] Fix text shown in unexpected locale (jenkinsci#9370)

Signed-off-by: Bob Du <[email protected]>
(cherry picked from commit 0ad6657)

core/src/main/java/hudson/model/Descriptor.java

@@ -1007,6 +1007,10 @@ public static URL getStaticHelpUrl(StaplerRequest req, Klass<?> c, String suffix
             if (url != null)    return url;
             url = c.getResource(base + '_' + locale.getLanguage() + ".html");
             if (url != null)    return url;
+            if (locale.getLanguage().equals("en")) {
+                url = c.getResource(base + ".html");
+                if (url != null)    return url;
+            }
         }
 
         // default

core/src/test/java/hudson/GetLocaleStaticHelpUrlTest.java

@@ -36,6 +36,7 @@
 import java.util.Enumeration;
 import java.util.Locale;
 import org.junit.jupiter.api.Test;
+import org.jvnet.hudson.test.Issue;
 import org.kohsuke.stapler.StaplerRequest;
 import org.kohsuke.stapler.lang.Klass;
 
@@ -191,6 +192,24 @@ public void getStaticHelpUrlAcceptZhResMore() {
         assertThatLocaleResourceIs(id, "help-id_zh_CN.html");
     }
 
+    @Issue("JENKINS-73246")
+    @Test
+    public void getStaticHelpUrlAcceptEnFirst() {
+        // Accept-Language: en-US,en;q=0.9,de;q=0.8
+        StaplerRequest req = mockStaplerRequest(
+                Locale.US,
+                Locale.ENGLISH,
+                Locale.GERMAN
+        );
+
+        Klass klass = mockKlass(
+                "help-id.html",
+                "help-id_de.html"
+        );
+        URL id = Descriptor.getStaticHelpUrl(req, klass, "-id");
+        assertThatLocaleResourceIs(id, "help-id.html");
+    }
+
     private StaplerRequest mockStaplerRequest(Locale... localeArr) {
         StaplerRequest req = mock(StaplerRequest.class);
         Enumeration<Locale> locales = Collections.enumeration(Arrays.asList(localeArr));