[UX] Allow keyboard layout selection

Fixes <#3998>.

This is an unpolished quickie but I've been letting this slip for too
long due to fancier keyboard interaction concepts.

frontend/ui/elements/common_settings_menu_table.lua

@@ -210,6 +210,10 @@ if Device:isAndroid() then
 end
 
 if Device:isTouchDevice() then
+    common_settings.keyboard_layout = {
+        text = _("Keyboard layout"),
+        sub_item_table = require("ui/elements/menu_keyboard_layout"),
+    }
     common_settings.taps_and_gestures = {
         text = _("Taps and gestures"),
     }

frontend/ui/elements/menu_keyboard_layout.lua

@@ -0,0 +1,19 @@
+local VirtualKeyboard = require("ui/widget/virtualkeyboard")
+--local _ = require("gettext")
+
+local keyboard_layout = G_reader_settings:readSetting("keyboard_layout")
+local sub_item_table = {}
+
+for k, _ in pairs(VirtualKeyboard.lang_to_keyboard_layout) do
+    table.insert(sub_item_table, {
+        text = k,
+        checked_func = function()
+            return G_reader_settings:readSetting("keyboard_layout") == k
+        end,
+        callback = function()
+            G_reader_settings:saveSetting("keyboard_layout", k)
+        end,
+    })
+end
+
+return sub_item_table

frontend/ui/elements/reader_menu_order.lua

@@ -57,6 +57,7 @@ local order = {
         "status_bar",
     },
     device = {
+        "keyboard_layout",
         "time",
         "battery",
         "autosuspend",

frontend/ui/widget/virtualkeyboard.lua

@@ -517,21 +517,21 @@ local VirtualKeyboard = FocusManager:new{
     bordersize = Size.border.default,
     padding = Size.padding.small,
     key_padding = Size.padding.default,
-}
 
-local lang_to_keyboard_layout = {
-    el = "el_keyboard",
-    en = "en_keyboard",
-    es = "es_keyboard",
-    fr = "fr_keyboard",
-    ja = "ja_keyboard",
-    pt_BR = "pt_keyboard",
-    ko_KR = "ko_KR_keyboard",
+    lang_to_keyboard_layout = {
+        el = "el_keyboard",
+        en = "en_keyboard",
+        es = "es_keyboard",
+        fr = "fr_keyboard",
+        ja = "ja_keyboard",
+        pt_BR = "pt_keyboard",
+        ko_KR = "ko_KR_keyboard",
+    },
 }
 
 function VirtualKeyboard:init()
-    local lang = G_reader_settings:readSetting("language")
-    local keyboard_layout = lang_to_keyboard_layout[lang] or lang_to_keyboard_layout["en"]
+    local lang = G_reader_settings:readSetting("keyboard_layout") or G_reader_settings:readSetting("language")
+    local keyboard_layout = self.lang_to_keyboard_layout[lang] or self.lang_to_keyboard_layout["en"]
     local keyboard = require("ui/data/keyboardlayouts/" .. keyboard_layout)
     self.KEYS = keyboard.keys
     self.shiftmode_keys = keyboard.shiftmode_keys