refactor: optimize translation unit handling in Crowdin script

- Introduced a new variable to track successfully translated units, improving clarity and efficiency in the processing logic.
- Updated the logic for combining existing and new translation units, ensuring accurate output and preventing unnecessary uploads when no new translations are available.

tools/translate_crowdin.py

@@ -775,11 +775,13 @@ def process_language(
                             f"source={u.source[:200]}\n")
         log.info("  Error details written to %s", err_path)
 
+    new_success = [u for u in translated_units if u.translated]
+
     if already_done and output_file.exists():
         existing_units = _parse_existing_output(output_file)
-        all_units = existing_units + [u for u in translated_units if u.translated]
+        all_units = existing_units + new_success
     else:
-        all_units = [u for u in translated_units if u.translated]
+        all_units = new_success
 
     if not all_units:
         if interrupted:
@@ -793,8 +795,10 @@ def process_language(
         output_file.write_text(xliff_content, encoding="utf-8")
         log.info("  Written: %s (%d units)", output_file.name, len(all_units))
 
-        if not skip_upload and not interrupted:
+        if not skip_upload and not interrupted and new_success:
             upload_xliff(output_file, crowdin_lang)
+        elif not new_success:
+            log.info("  No new translations this run, skipping upload")
 
     if interrupted:
         raise KeyboardInterrupt