mod_cloud_notify_encrypted: Ensure body substring remains valid UTF-8 The `body:sub()` call risks splitting the string in the middle of a multi-byte UTF-8 sequence. This should have been caught by util.stanza validation, but that would have caused some havoc, at the very least causing the notification to not be sent. There have been no reports of this happening. Likely because this module isn't widely deployed among users with languages that use many longer UTF-8 sequences. The util.encodings.utf8.valid() function is O(n) where only the last sequence really needs to be checked, but it's in C and expected to be fast.

# Introduction

This module adds support for advertising the language used in a room.

# Configuring

``` {.lua}
Component "rooms.example.net" "muc"
modules_enabled = {
    "muc_lang";
}
```

The room language is specified in a new field in the room configuration
dialog, accessible through compatible clients.

Use [language codes](https://en.wikipedia.org/wiki/ISO_639) like `en`,
`fr`, `de` etc.

# Compatibility

Meant for use with Prosody 0.10.x

Native support was [added in Prosody
trunk/0.11](https://hg.prosody.im/trunk/rev/9c90cd2fc4c3), so there is
no need for this module.