Add additional known obscured subjects from k-9/thunderbird-android.

These additional subjects were extracted from the thunderbird-android
source (which is inherited from k-9).

The extraction was done with:

```
git clone https://github.com/thunderbird/thunderbird-android/
cd thunderbird-android/legacy/ui/legacy/src/main/res
grep string\ name=\"encrypted_subject values-*/strings.xml | cut -f2 -d'>' | cut -f1 -d'<' | sort -u | sed -e 's/^/    "/' -e 's/$/",/'
```

(i did need to clean up one line's escaping to pass the linter's
expectations)

See also https://github.com/thunderbird/thunderbird-android/issues/8011

chatmaild/src/chatmaild/filtermail.py

@@ -14,6 +14,64 @@ from aiosmtpd.controller import Controller
 
 from .config import read_config
 
+"""Generated from deltachat, draft-ietf-lamps-header-protection, and
+encrypted_subject localizations in
+https://github.com/thunderbird/thunderbird-android/
+"""
+common_encrypted_subjects = {
+    "...",
+    "[...]",
+    "암호화된 메시지",
+    "Ĉifrita mesaĝo",
+    "Courriel chiffré",
+    "Dulrituð skilaboð",
+    "Encrypted Message",
+    "Fersifere berjocht",
+    "Kemennadenn enrineget",
+    "Krüptitud kiri",
+    "Krypterat meddelande",
+    "Krypteret besked",
+    "Kryptert melding",
+    "Mensagem criptografada",
+    "Mensagem encriptada",
+    "Mensaje cifrado",
+    "Mensaxe cifrada",
+    "Mesaj Criptat",
+    "Mesazh i Fshehtëzuar",
+    "Messaggio criptato",
+    "Messaghju cifratu",
+    "Missatge encriptat",
+    "Neges wedi'i Hamgryptio",
+    "Pesan terenkripsi",
+    "Salattu viesti",
+    "Şifreli İleti",
+    "Šifrēta ziņa",
+    "Šifrirana poruka",
+    "Šifrirano sporočilo",
+    "Šifruotas laiškas",
+    "Tin nhắn được mã hóa",
+    "Titkosított üzenet",
+    "Verschlüsselte Nachricht",
+    "Versleuteld bericht",
+    "Zašifrovaná zpráva",
+    "Zaszyfrowana wiadomość",
+    "Zifratu mezua",
+    "Κρυπτογραφημένο μήνυμα",
+    "Зашифроване повідомлення",
+    "Зашифрованное сообщение",
+    "Зашыфраваны ліст",
+    "Криптирано съобщение",
+    "Шифрована порука",
+    "დაშიფრული წერილი",
+    "הודעה מוצפנת",
+    "پیام رمزنگاری‌شده",
+    "رسالة مشفّرة",
+    "എൻക്രിപ്റ്റുചെയ്‌ത സന്ദേശം",
+    "加密邮件",
+    "已加密的訊息",
+    "暗号化されたメッセージ",
+}
+
 
 def check_openpgp_payload(payload: bytes):
     """Checks the OpenPGP payload.
@@ -111,7 +169,7 @@ def check_encrypted(message):
     """
     if not message.is_multipart():
         return False
-    if message.get("subject") not in {"...", "[...]"}:
+    if message.get("subject") not in common_encrypted_subjects:
         return False
     if message.get_content_type() != "multipart/encrypted":
         return False

chatmaild/src/chatmaild/tests/test_filtermail.py

@@ -4,6 +4,7 @@ from chatmaild.filtermail import (
     SendRateLimiter,
     check_armored_payload,
     check_encrypted,
+    common_encrypted_subjects,
 )
 
 
@@ -54,7 +55,7 @@ def test_filtermail_no_encryption_detection(maildata):
 
 
 def test_filtermail_encryption_detection(maildata):
-    for subject in ("...", "[...]"):
+    for subject in common_encrypted_subjects:
         msg = maildata(
             "encrypted.eml",
             from_addr="1@example.org",