Better handling of plurals during .po validation

Now any of the plurals being missing will count as an Empty translation,
and for looking at tags, the two English strings and all the translated
strings are mooshed together.

i18n/tests/test_validate.py

@@ -93,13 +93,21 @@ def check_messages(filename):
             problems.append(("Non-BMP char", msg.msgid, msg.msgstr))
 
         if msg.msgid_plural:
-            # Skip plurals, I don't know how the tags relate.
-            continue
-        if not msg.msgstr:
-            problems.append(("Empty translation", msg.msgid))
+            # Plurals: two strings in, N strings out.
+            source = msg.msgid + " | " + msg.msgid_plural
+            translation = " | ".join(v for k,v in sorted(msg.msgstr_plural.items()))
+            empty = any(not t.strip() for t in msg.msgstr_plural.values())
         else:
-            id_tags = tags_in_string(msg.msgid)
-            tx_tags = tags_in_string(msg.msgstr)
+            # Singular: just one string in and one string out.
+            source = msg.msgid
+            translation = msg.msgstr
+            empty = not msg.msgstr.strip()
+
+        if empty:
+            problems.append(("Empty translation", source))
+        else:
+            id_tags = tags_in_string(source)
+            tx_tags = tags_in_string(translation)
             if id_tags != tx_tags:
                 id_has = u", ".join(u'"{}"'.format(t) for t in id_tags - tx_tags)
                 tx_has = u", ".join(u'"{}"'.format(t) for t in tx_tags - id_tags)
@@ -111,8 +119,8 @@ def check_messages(filename):
                     diff = u"{} added".format(tx_has)
                 problems.append((
                     "Different tags in source and translation",
-                    msg.msgid,
-                    msg.msgstr,
+                    source,
+                    translation,
                     diff
                 ))