[i18n] Enable Arabic and Esperanto (#5515)

Unfortunately I missed that Arabic has had a few hundred translated strings for a couple of months now.

Cf. <https://github.com/koreader/koreader/issues/5359#issuecomment-544460031>.

frontend/ui/language.lua

@@ -11,6 +11,7 @@ local Language = {
         ca = "Catalá",
         cs_CZ = "Čeština",
         de = "Deutsch",
+        eo = "Esperanto",
         es = "Español",
         eu = "Euskara",
         fr = "Français",
@@ -82,6 +83,7 @@ function Language:getLangMenuTable()
                 self:genLanguageSubItem("ca"),
                 self:genLanguageSubItem("cs_CZ"),
                 self:genLanguageSubItem("de"),
+                self:genLanguageSubItem("eo"),
                 self:genLanguageSubItem("es"),
                 self:genLanguageSubItem("eu"),
                 self:genLanguageSubItem("fr"),
@@ -98,8 +100,8 @@ function Language:getLangMenuTable()
                 self:genLanguageSubItem("sv"),
                 self:genLanguageSubItem("vi"),
                 self:genLanguageSubItem("tr"),
-                --self:genLanguageSubItem("vi_VN"),
-                --self:genLanguageSubItem(""ar_AA"),
+                self:genLanguageSubItem("vi_VN"),
+                self:genLanguageSubItem("ar_AA"),
                 self:genLanguageSubItem("bg_BG"),
                 --self:genLanguageSubItem("bn"),
                 self:genLanguageSubItem("el"),