drop bad machine translations of Serbian

I have modified the Weblate settings to use the v3 Google Translate API instead of the older one, which results in placeholders being handled correctly. Dropping the bad translations makes way for correct ones to be automatically generated by Weblate.

cli/po-tools.py

@@ -1,3 +1,4 @@
+import re
 import sys
 
 from babel.messages.pofile import read_po, write_po
@@ -76,6 +77,28 @@
     with open(po_path, 'wb') as po:
         write_po(po, catalog, width=0)
 
+elif sys.argv[1] == 'drop-translations-matching':
+    drop_pattern = sys.argv[2]
+    po_path = sys.argv[3]
+    print(f'dropping translations matching {drop_pattern!r} in PO file {po_path}')
+    # read PO file
+    lang = po_path.rsplit('/', 1)[-1].split('.', 1)[0]
+    with open(po_path, 'rb') as po:
+        catalog = read_po(po, locale=lang)
+    # look for translations that match the pattern, and drop them
+    drop_re = re.compile(drop_pattern)
+    for m in catalog:
+        if isinstance(m.string, tuple):
+            m.string = tuple(
+                '' if drop_re.search(s) else s
+                for s in m.string
+            )
+        else:
+            m.string = '' if drop_re.search(m.string) else m.string
+    # write back
+    with open(po_path, 'wb') as po:
+        write_po(po, catalog, width=0)
+
 elif sys.argv[1] == 'fuzz':
     po_path = sys.argv[2]
     old_msg = sys.argv[3]