Allow customizing instance languages

config/description.exs

@@ -1052,6 +1052,15 @@ config :pleroma, :config_description, [
         description:
           "Minimum required age (in days) for users to create account. Only used if birthday is required.",
         suggestions: [6570]
+      },
+      %{
+        key: :languages,
+        type: {:list, :string},
+        description:
+          "Languages to be exposed in /api/v1/instance. Should be in the format of BCP47 language codes.",
+        suggestions: [
+          "en"
+        ]
       }
     ]
   },

lib/pleroma/web/mastodon_api/views/instance_view.ex

@@ -27,7 +27,7 @@ defmodule Pleroma.Web.MastodonAPI.InstanceView do
       thumbnail:
         URI.merge(Pleroma.Web.Endpoint.url(), Keyword.get(instance, :instance_thumbnail))
         |> to_string,
-      languages: ["en"],
+      languages: Keyword.get(instance, :languages, ["en"]),
       registrations: Keyword.get(instance, :registrations_open),
       approval_required: Keyword.get(instance, :account_approval_required),
       # Extra (not present in Mastodon):

test/pleroma/web/mastodon_api/controllers/instance_controller_test.exs

@@ -92,4 +92,18 @@ defmodule Pleroma.Web.MastodonAPI.InstanceControllerTest do
 
     assert ["peer1.com", "peer2.com"] == Enum.sort(result)
   end
+
+  test "instance languages", %{conn: conn} do
+    assert %{"languages" => ["en"]} =
+             conn
+             |> get("/api/v1/instance")
+             |> json_response_and_validate_schema(200)
+
+    clear_config([:instance, :languages], ["aa", "bb"])
+
+    assert %{"languages" => ["aa", "bb"]} =
+             conn
+             |> get("/api/v1/instance")
+             |> json_response_and_validate_schema(200)
+  end
 end