pad: Use `null` as default for `lang` option

It doesn't make sense to override the browser's language with `en-gb`
by default.

Note that this change has no effect due to a bug in how pad options
are processed; that bug will be fixed in a future commit.

doc/docker.md

@@ -121,7 +121,7 @@ If your database needs additional settings, you will have to use a personalized
 | `PAD_OPTIONS_RTL`                |             | `false` |
 | `PAD_OPTIONS_ALWAYS_SHOW_CHAT`   |             | `false` |
 | `PAD_OPTIONS_CHAT_AND_USERS`     |             | `false` |
-| `PAD_OPTIONS_LANG`               |             | `en-gb` |
+| `PAD_OPTIONS_LANG`               |             | `null`  |
 
 
 ### Shortcuts

settings.json.docker

@@ -239,7 +239,7 @@
     "rtl":              "${PAD_OPTIONS_RTL:false}",
     "alwaysShowChat":   "${PAD_OPTIONS_ALWAYS_SHOW_CHAT:false}",
     "chatAndUsers":     "${PAD_OPTIONS_CHAT_AND_USERS:false}",
-    "lang":             "${PAD_OPTIONS_LANG:en-gb}"
+    "lang":             "${PAD_OPTIONS_LANG:null}"
   },
 
   /*

settings.json.template

@@ -240,7 +240,7 @@
     "rtl":              false,
     "alwaysShowChat":   false,
     "chatAndUsers":     false,
-    "lang":             "en-gb"
+    "lang":             null
   },
 
   /*

src/node/utils/Settings.js

@@ -170,7 +170,7 @@ exports.padOptions = {
   rtl: false,
   alwaysShowChat: false,
   chatAndUsers: false,
-  lang: 'en-gb',
+  lang: null,
 };
 
 /**