feat: surface raw Tesseract diacritics message at debug level

When Tesseract reports a page with many diacritics, OCRmyPDF rewrites the
message to "lots of diacritics - possibly poor OCR", which hid the
original wording. Keep the interpreted hint but also emit Tesseract's raw
line at debug verbosity (-v 1) so users can see exactly what Tesseract
reported.

Closes #1566.

docs/releasenotes/version17.md

@@ -76,6 +76,10 @@
   OCRmyPDF now also logs which rasterizer rendered each page at debug verbosity
   (``-v 1``), and the ``--rasterizer`` help text explains the OCR-quality
   trade-off, to make such reports easier to diagnose. {issue}`1439`
+- When Tesseract reports a page with many diacritics, OCRmyPDF still logs its
+  interpreted "lots of diacritics - possibly poor OCR" hint, but now also emits
+  Tesseract's raw message at debug verbosity (``-v 1``) so the original wording
+  is available for diagnosis. {issue}`1566`
 
 ## v17.5.0
 

src/ocrmypdf/_exec/tesseract.py

@@ -297,6 +297,10 @@ def tesseract_log_output(stream: bytes) -> None:
             continue
         elif 'diacritics' in line:
             tlog.warning("lots of diacritics - possibly poor OCR")
+            # Surface the raw Tesseract message at debug level so users can see
+            # exactly what Tesseract reported (e.g. the affected count) without
+            # losing the interpreted hint above (#1566).
+            tlog.debug(line.strip())
         elif line.startswith('OSD: Weak margin'):
             tlog.warning("unsure about page orientation")
         elif 'Error in pixScanForForeground' in line:

tests/test_tesseract.py

@@ -141,6 +141,14 @@ def test_tesseract_log_output(caplog, in_, logged):
         assert logged in caplog.text
 
 
+def test_tesseract_log_output_diacritics_raw(caplog):
+    """Diacritics branch keeps the interpreted hint and surfaces raw (#1566)."""
+    caplog.set_level(logging.DEBUG)
+    tesseract.tesseract_log_output(b'lots of diacritics blah blah')
+    assert 'possibly poor OCR' in caplog.text  # interpreted hint retained
+    assert 'lots of diacritics blah blah' in caplog.text  # raw message surfaced
+
+
 def test_tesseract_log_output_raises(caplog):
     with pytest.raises(tesseract.TesseractConfigError):
         tesseract.tesseract_log_output(b'parameter not found: moo')