Change ArgosTranslate strategy for dealing with nil from-language

Instead of choosing a fallback language, we just return the input, supposedly translated from the target language.
This gives us a much faster response, so you can immedialty choose the correct from language yourself in pleroma-fe.

Some other cleanup and improvements to the docs are also done.

config/config.exs

@@ -885,7 +885,6 @@
 config :pleroma, :argos_translate,
   command_argos_translate: "argos-translate",
   command_argospm: "argospm",
-  fallback_language: "en",
   strip_html: true
 
 # Import environment specific config. This must remain at the bottom

docs/docs/configuration/cheatsheet.md

@@ -1119,7 +1119,7 @@ Each job has these settings:
 ### Translation Settings
 
 Settings to automatically translate statuses for end users. Currently supported
-translation services are DeepL and LibreTranslate.
+translation services are DeepL and LibreTranslate. The supported command line tool is [Argos Translate](https://github.com/argosopentech/argos-translate).
 
 Translations are available at `/api/v1/statuses/:id/translations/:language`, where
 `language` is the target language code (e.g `en`)
@@ -1128,7 +1128,7 @@ Translations are available at `/api/v1/statuses/:id/translations/:language`, whe
 
 - `:enabled` - enables translation
 - `:module` - Sets module to be used
-  - Either `Pleroma.Akkoma.Translators.DeepL` or `Pleroma.Akkoma.Translators.LibreTranslate`
+  - Either `Pleroma.Akkoma.Translators.DeepL`, `Pleroma.Akkoma.Translators.LibreTranslate`, or `Pleroma.Akkoma.Translators.ArgosTranslate`
 
 ### `:deepl`
 
@@ -1143,9 +1143,6 @@ Translations are available at `/api/v1/statuses/:id/translations/:language`, whe
 
 ### `:argos_translate`
 
-[Argos Translate](https://github.com/argosopentech/argos-translate) is the library used by Libre Translate and can run as a command line tool. It's more basic than Libre Translate as it doesn't provide a way to properly handle html or language detection.
-
 - `:command_argos_translate` - command for `argos-translate`. Can be the command if it's in your PATH, or the full path to the file  (default: `argos-translate`).
 - `:command_argospm` - command for `argospm`. Can be the command if it's in your PATH, or the full path to the file (default: `argospm`).
-- `:fallback_language` - When no language is provided to translate from, this language will be used. Must be a two letter langage code from a language you have installed (default: `en`).
-- `:strip_html` - Strip html from the post before translating the text (default: `true`).
+- `:strip_html` - Strip html from the post before translating it (default: `true`).

lib/pleroma/akkoma/translators/argos_translate.ex

@@ -11,8 +11,8 @@ defp argospm do
     Config.get([:argos_translate, :command_argospm])
   end
 
-  defp fallback_language do
-    Config.get([:argos_translate, :fallback_language])
+  defp strip_html? do
+    Config.get([:argos_translate, :strip_html])
   end
 
   defp safe_languages() do
@@ -85,23 +85,24 @@ defp htmlify_response(string, true) do
   defp htmlify_response(string, _), do: string
 
   @impl Pleroma.Akkoma.Translator
-  def translate(string, from_language, to_language) do
-    strip_html = Config.get([:argos_translate, :strip_html])
+  def translate(string, nil, to_language) do
     # Akkoma's Pleroma-fe expects us to detect the source language automatically.
     # Argos-translate doesn't have that option (yet?)
     #     see <https://github.com/argosopentech/argos-translate/issues/9>
-    # For now we choose a fallback source language from settings.
+    # For now we return the text unchanged, supposedly translated from the target language.
     # Afterwards people get the option to overwrite the source language from a dropdown.
-    from_language = from_language || fallback_language()
-    to_language = to_language || fallback_language()
+    {:ok, to_language, string}
+  end
+
+  def translate(string, from_language, to_language) do
     # Argos Translate doesn't properly translate HTML (yet?)
     # For now we give admins the option to strip the html before translating
     # Note that we have to add some html back to the response afterwards
-    string = clean_string(string, strip_html)
+    string = clean_string(string, strip_html?())
 
     with {translated, 0} <-
            safe_translate(string, from_language, to_language) do
-      {:ok, from_language, translated |> htmlify_response(strip_html)}
+      {:ok, from_language, translated |> htmlify_response(strip_html?())}
     else
       {response, _} -> {:error, "ArgosTranslate failed to translate (#{response})"}
     end

test/pleroma/akkoma/translators/argos_translate_test.exs

@@ -27,19 +27,11 @@ test "it lists available languages" do
     assert [%{code: "en", name: "en"}, %{code: "nl", name: "nl"}] = dest_langs |> Enum.sort()
   end
 
-  test "it translates from default language when no language is set" do
-    translation_response =
-      with_mock System, [:passthrough],
-        cmd: fn "argos-translate_test", ["--from-lang", "en", "--to-lang", "fr", "blabla"], _ ->
-          {"yadayada", 0}
-        end do
-        ArgosTranslate.translate("blabla", nil, "fr")
+  test "it translates from the to language when no language is set and returns the text unchanged" do
+    assert {:ok, "nl", "blabla"} = ArgosTranslate.translate("blabla", nil, "nl")
   end
 
-    assert {:ok, "en", "yadayada"} = translation_response
-  end
-
-  test "it translates from the provided language" do
+  test "it translates from the provided language if provided" do
     translation_response =
       with_mock System, [:passthrough],
         cmd: fn "argos-translate_test", ["--from-lang", "nl", "--to-lang", "en", "blabla"], _ ->