diff --git a/.mokogitea/workflows/pr-check.yml b/.mokogitea/workflows/pr-check.yml
index e2c82ef..9d0cb35 100644
--- a/.mokogitea/workflows/pr-check.yml
+++ b/.mokogitea/workflows/pr-check.yml
@@ -105,6 +105,19 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
+      - name: Check for merge conflict markers
+        run: |
+          CONFLICTS=$(grep -rn '<<<<<<< \|>>>>>>> \|^=======$' --include='*.php' --include='*.xml' --include='*.css' --include='*.js' --include='*.json' --include='*.md' --include='*.yml' --include='*.yaml' --include='*.ini' --include='*.txt' . 2>/dev/null | grep -v '.git/' || true)
+          if [ -n "$CONFLICTS" ]; then
+            echo "::error::Merge conflict markers found in source files"
+            echo "## Conflict Markers Found" >> $GITHUB_STEP_SUMMARY
+            echo '```' >> $GITHUB_STEP_SUMMARY
+            echo "$CONFLICTS" >> $GITHUB_STEP_SUMMARY
+            echo '```' >> $GITHUB_STEP_SUMMARY
+            exit 1
+          fi
+          echo "No conflict markers found"
+
       - name: Detect platform
         id: platform
         run: |
@@ -183,6 +196,101 @@ jobs:
               ;;
           esac
 
+      - name: Validate Joomla language files
+        if: steps.platform.outputs.platform == 'joomla'
+        run: |
+          ERRORS=0
+          WARNINGS=0
+
+          # Find all .ini language files
+          INI_FILES=$(find . -path "*/language/*/*.ini" -not -path "./.git/*" 2>/dev/null)
+          if [ -z "$INI_FILES" ]; then
+            echo "No .ini language files found — skipping"
+            exit 0
+          fi
+
+          echo "Found $(echo "$INI_FILES" | wc -l) language file(s)"
+
+          for FILE in $INI_FILES; do
+            FNAME=$(basename "$FILE")
+            LINENUM=0
+            SEEN_KEYS=""
+
+            while IFS= read -r line || [ -n "$line" ]; do
+              LINENUM=$((LINENUM + 1))
+
+              # Skip empty lines and comments
+              [ -z "$line" ] && continue
+              echo "$line" | grep -qE '^\s*;' && continue
+              echo "$line" | grep -qE '^\s*$' && continue
+
+              # Must match KEY="VALUE" format
+              if ! echo "$line" | grep -qE '^[A-Z_][A-Z0-9_]*=".*"$'; then
+                echo "::error file=${FILE},line=${LINENUM}::Malformed line: ${line}"
+                ERRORS=$((ERRORS + 1))
+                continue
+              fi
+
+              # Extract key and check for duplicates
+              KEY=$(echo "$line" | sed 's/=.*//')
+              if echo "$SEEN_KEYS" | grep -qx "$KEY"; then
+                echo "::error file=${FILE},line=${LINENUM}::Duplicate key: ${KEY}"
+                ERRORS=$((ERRORS + 1))
+              fi
+              SEEN_KEYS="${SEEN_KEYS}
+          ${KEY}"
+            done < "$FILE"
+
+            echo "  ${FILE}: checked ${LINENUM} lines"
+          done
+
+          # Cross-check en-GB vs en-US key consistency
+          GB_DIR=$(find . -path "*/language/en-GB" -type d -not -path "./.git/*" 2>/dev/null | head -1)
+          US_DIR=$(find . -path "*/language/en-US" -type d -not -path "./.git/*" 2>/dev/null | head -1)
+
+          if [ -n "$GB_DIR" ] && [ -n "$US_DIR" ]; then
+            for GB_FILE in "$GB_DIR"/*.ini; do
+              [ ! -f "$GB_FILE" ] && continue
+              FNAME=$(basename "$GB_FILE")
+              US_FILE="$US_DIR/$FNAME"
+              [ ! -f "$US_FILE" ] && continue
+
+              GB_KEYS=$(grep -oP '^[A-Z_][A-Z0-9_]*(?==)' "$GB_FILE" 2>/dev/null | sort)
+              US_KEYS=$(grep -oP '^[A-Z_][A-Z0-9_]*(?==)' "$US_FILE" 2>/dev/null | sort)
+
+              # Keys in en-GB but not en-US
+              MISSING_US=$(comm -23 <(echo "$GB_KEYS") <(echo "$US_KEYS"))
+              if [ -n "$MISSING_US" ]; then
+                echo "::warning::Keys in en-GB/$FNAME but missing from en-US/$FNAME:"
+                echo "$MISSING_US" | while read -r k; do echo "  - $k"; done
+                WARNINGS=$((WARNINGS + 1))
+              fi
+
+              # Keys in en-US but not en-GB
+              MISSING_GB=$(comm -13 <(echo "$GB_KEYS") <(echo "$US_KEYS"))
+              if [ -n "$MISSING_GB" ]; then
+                echo "::warning::Keys in en-US/$FNAME but missing from en-GB/$FNAME:"
+                echo "$MISSING_GB" | while read -r k; do echo "  - $k"; done
+                WARNINGS=$((WARNINGS + 1))
+              fi
+            done
+          fi
+
+          {
+            echo "### Language File Validation"
+            echo "| Metric | Count |"
+            echo "|---|---|"
+            echo "| Files checked | $(echo "$INI_FILES" | wc -l) |"
+            echo "| Errors | ${ERRORS} |"
+            echo "| Warnings | ${WARNINGS} |"
+          } >> $GITHUB_STEP_SUMMARY
+
+          if [ "$ERRORS" -gt 0 ]; then
+            echo "::error::Language validation failed with ${ERRORS} error(s)"
+            exit 1
+          fi
+          echo "Language files: OK (${WARNINGS} warning(s))"
+
       - name: Check changelog has unreleased entry
         run: |
           if [ ! -f "CHANGELOG.md" ]; then