Files: Improve uploaded file format detection

Change ordering when detected extension matches configured format. For
example we need to prefer monolingual PO parser for monolingual PO
components, otherwise it is parsed as bilingual and that leads to no
matches.

Fixes #4249

weblate/formats/auto.py

@@ -39,10 +39,18 @@ def detect_filename(filename):
 
 def try_load(filename, content, original_format, template_store):
     """Try to load file by guessing type."""
+    # Start with original format and translate-toolkit based autodetection
     formats = [original_format, AutodetectFormat]
     detected_format = detect_filename(filename)
-    if detected_format is not None:
-        formats.insert(0, detected_format)
+    if detected_format is not None and detected_format != original_format:
+        # Insert detected filename into most probable location. In case the extension
+        # matches original, insert it after that as it is more likely that the upload
+        # is in the original format (for example if component is monolingual PO file,
+        # the uploaded PO file is more likely to be monolingual as well).
+        formats.insert(
+            1 if detected_format.extension == original_format.extension else 0,
+            detected_format,
+        )
     failure = Exception("Bug!")
     for file_format in formats:
         if file_format.monolingual in (True, None) and template_store: