diff --git a/pmd-cli/src/test/java/net/sourceforge/pmd/cli/CpdCliTest.java b/pmd-cli/src/test/java/net/sourceforge/pmd/cli/CpdCliTest.java
index 8a9d4758de..b60b511d8e 100644
--- a/pmd-cli/src/test/java/net/sourceforge/pmd/cli/CpdCliTest.java
+++ b/pmd-cli/src/test/java/net/sourceforge/pmd/cli/CpdCliTest.java
@@ -87,6 +87,12 @@ class CpdCliTest extends BaseCliTest {
         result.checkStdErr(containsString("[main] INFO net.sourceforge.pmd.cli - Log level is at TRACE"));
     }
 
+    @Test
+    void debugLoggingShouldMentionLanguage() throws Exception {
+        final CliExecutionResult result = runCli(VIOLATIONS_FOUND, "--minimum-tokens", "34", "--dir", SRC_DIR, "--debug");
+        result.checkStdErr(containsString("Created new FileCollector with LanguageVersionDiscoverer(LanguageRegistry(java))"));
+    }
+
     @Test
     void defaultLogging() throws Exception {
         CliExecutionResult result = runCliSuccessfully("--minimum-tokens", "340", "--dir", SRC_DIR);
@@ -112,6 +118,13 @@ class CpdCliTest extends BaseCliTest {
         result.checkStdErr(containsString("Usage: pmd cpd"));
     }
 
+    @Test
+    void testWrongCliOptionResultsInErrorLogging() throws Exception {
+        // --ignore-identifiers doesn't take an argument anymore - it is interpreted as a file for inputPaths
+        final CliExecutionResult result = runCli(VIOLATIONS_FOUND, "--minimum-tokens", "34", "--dir", SRC_DIR, "--ignore-identifiers", "false");
+        result.checkStdErr(containsString("No such file false"));
+    }
+
     @Test
     void testFindJavaDuplication() throws Exception {
         runCli(VIOLATIONS_FOUND, "--minimum-tokens", "7", "--dir", SRC_DIR)
@@ -125,7 +138,7 @@ class CpdCliTest extends BaseCliTest {
      */
     @Test
     void testIgnoreIdentifiers() throws Exception {
-        runCli(VIOLATIONS_FOUND, "--minimum-tokens", "34", "--dir", SRC_DIR, "--ignore-identifiers")
+        runCli(VIOLATIONS_FOUND, "--minimum-tokens", "34", "--dir", SRC_DIR, "--ignore-identifiers", "false", "--debug")
             .verify(result -> result.checkStdOut(containsString(
                     "Found a 14 line (89 tokens) duplication"
         )));
diff --git a/pmd-core/src/main/java/net/sourceforge/pmd/lang/LanguageVersionDiscoverer.java b/pmd-core/src/main/java/net/sourceforge/pmd/lang/LanguageVersionDiscoverer.java
index ad8fef10b8..b4e5920480 100644
--- a/pmd-core/src/main/java/net/sourceforge/pmd/lang/LanguageVersionDiscoverer.java
+++ b/pmd-core/src/main/java/net/sourceforge/pmd/lang/LanguageVersionDiscoverer.java
@@ -168,4 +168,11 @@ public class LanguageVersionDiscoverer {
     public void onlyRecognizeLanguages(LanguageRegistry lang) {
         this.languageRegistry = Objects.requireNonNull(lang);
     }
+
+    @Override
+    public String toString() {
+        return "LanguageVersionDiscoverer(" + languageRegistry
+                + (forcedVersion != null ? ",forcedVersion=" + forcedVersion : "")
+                + ")";
+    }
 }
diff --git a/pmd-core/src/main/java/net/sourceforge/pmd/lang/document/FileCollector.java b/pmd-core/src/main/java/net/sourceforge/pmd/lang/document/FileCollector.java
index 20ec3aff72..6cc0ff5006 100644
--- a/pmd-core/src/main/java/net/sourceforge/pmd/lang/document/FileCollector.java
+++ b/pmd-core/src/main/java/net/sourceforge/pmd/lang/document/FileCollector.java
@@ -70,6 +70,7 @@ public final class FileCollector implements AutoCloseable {
         this.discoverer = discoverer;
         this.reporter = reporter;
         this.outerFsPath = outerFsPath;
+        LOG.debug("Created new FileCollector with {}", discoverer);
     }
 
     public void setRecursive(boolean collectFilesRecursively) {