Add Duala (dua) (#375)

Downstream request:
https://phabricator.wikimedia.org/T372173

data/langdb.yaml

@@ -203,6 +203,7 @@ languages:
   dsb: [Latn, [EU], dolnoserbski]
   dtp: [Latn, [AS], Dusun Bundu-liwan]
   dty: [Deva, [AS], डोटेली]
+  dua: [Latn, [AF], Duálá]
   dv: [Thaa, [AS], ދިވެހިބަސް]
   dyu: [Latn, [AF], Julakan]
   dz: [Tibt, [AS], ཇོང་ཁ]

data/language-data.json

@@ -1218,6 +1218,13 @@
             ],
             "डोटेली"
         ],
+        "dua": [
+            "Latn",
+            [
+                "AF"
+            ],
+            "Duálá"
+        ],
         "dv": [
             "Thaa",
             [
@@ -5768,6 +5775,7 @@
             "ff",
             "bkm",
             "bas",
+            "dua",
             "ar",
             "ksf",
             "ken",