Prepare for selecting languages

UI language is stored in user settings for authenticated users;
otherwise is only stored in the current model (not persisted).

modules/webapp/src/main/elm/Messages.elm

@@ -0,0 +1,87 @@
+module Messages exposing
+    ( Messages
+    , fromIso2
+    , get
+    , toIso2
+    )
+
+import Messages.App
+import Messages.LoginPage
+import UiLanguage exposing (UiLanguage(..))
+
+
+{-| The messages record contains all strings used in the application.
+-}
+type alias Messages =
+    { lang : UiLanguage
+    , iso2 : String
+    , label : String
+    , flagIcon : String
+    , app : Messages.App.Texts
+    , login : Messages.LoginPage.Texts
+    }
+
+
+get : UiLanguage -> Messages
+get lang =
+    case lang of
+        English ->
+            gb
+
+        German ->
+            de
+
+
+{-| Get a ISO-3166-1 code of the given lanugage.
+-}
+toIso2 : UiLanguage -> String
+toIso2 lang =
+    get lang |> .iso2
+
+
+{-| Return the UiLanguage from given iso2 code. If the iso2 code is not
+known, return Nothing.
+-}
+readIso2 : String -> Maybe UiLanguage
+readIso2 iso =
+    let
+        isIso lang =
+            iso == toIso2 lang
+    in
+    List.filter isIso UiLanguage.all
+        |> List.head
+
+
+{-| return the language from the given iso2 code. if the iso2 code is
+not known, return English as a default.
+-}
+fromIso2 : String -> UiLanguage
+fromIso2 iso =
+    readIso2 iso
+        |> Maybe.withDefault English
+
+
+
+--- Messages Definitions
+
+
+gb : Messages
+gb =
+    { lang = English
+    , iso2 = "gb"
+    , label = "English"
+    , flagIcon = "flag-icon flag-icon-gb"
+    , app = Messages.App.gb
+    , login = Messages.LoginPage.gb
+    }
+
+
+de : Messages
+de =
+    { lang = German
+    , iso2 = "de"
+    , label = "Deutsch"
+    , flagIcon = "flag-icon flag-icon-de"
+    , app = Messages.App.de
+    , login = Messages.LoginPage.de
+    }