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diff --git a/lib/pleroma/web/plugs/set_locale_plug.ex b/lib/pleroma/web/plugs/set_locale_plug.ex
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index 000000000..d9d24b93f
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+++ b/lib/pleroma/web/plugs/set_locale_plug.ex
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+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2020 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+# NOTE: this module is based on https://github.com/smeevil/set_locale
+defmodule Pleroma.Web.Plugs.SetLocalePlug do
+  import Plug.Conn, only: [get_req_header: 2, assign: 3]
+
+  def init(_), do: nil
+
+  def call(conn, _) do
+    locale = get_locale_from_header(conn) || Gettext.get_locale()
+    Gettext.put_locale(locale)
+    assign(conn, :locale, locale)
+  end
+
+  defp get_locale_from_header(conn) do
+    conn
+    |> extract_accept_language()
+    |> Enum.find(&supported_locale?/1)
+  end
+
+  defp extract_accept_language(conn) do
+    case get_req_header(conn, "accept-language") do
+      [value | _] ->
+        value
+        |> String.split(",")
+        |> Enum.map(&parse_language_option/1)
+        |> Enum.sort(&(&1.quality > &2.quality))
+        |> Enum.map(& &1.tag)
+        |> Enum.reject(&is_nil/1)
+        |> ensure_language_fallbacks()
+
+      _ ->
+        []
+    end
+  end
+
+  defp supported_locale?(locale) do
+    Pleroma.Web.Gettext
+    |> Gettext.known_locales()
+    |> Enum.member?(locale)
+  end
+
+  defp parse_language_option(string) do
+    captures = Regex.named_captures(~r/^\s?(?<tag>[\w\-]+)(?:;q=(?<quality>[\d\.]+))?$/i, string)
+
+    quality =
+      case Float.parse(captures["quality"] || "1.0") do
+        {val, _} -> val
+        :error -> 1.0
+      end
+
+    %{tag: captures["tag"], quality: quality}
+  end
+
+  defp ensure_language_fallbacks(tags) do
+    Enum.flat_map(tags, fn tag ->
+      [language | _] = String.split(tag, "-")
+      if Enum.member?(tags, language), do: [tag], else: [tag, language]
+    end)
+  end
+end