These instructions will build TheFae's modded Mudlet.  Alternatively you can use the current release of the official Mudlet binary for Linux found here..  https://www.mudlet.org/
The github repo no longer exists but here is its contents with minor modifications to the install steps so you can still build TheFae's modded Mudlet if you want.

Download and extract http://botman.nz/ModdedMudlet.zip

Open a terminal where you downloaded the zip and type unzip -x ModdedMudlet.zip
Type chmod +x ./setup-debian.sh && ./setup-debian.sh
Type chmod +x ./build-mudlet.sh && ./build-mudlet.sh

At this point it will want to build Mudlet for you and will ask you some questions.  Select option 1 to build master.  If you select option 2 it will build the default Mudlet not the modded Mudlet.
It will also ask how many of the available processors to use during the build.  The higher the number, the faster it will build.  It will finish by briefly test running Mudlet and you should see it flash up for a second.  If instead the build ends with errors, you will most likely need to downgrade your Ubuntu to no newer than 16.04.  The error can be fixed if you are sufficiently advanced with Linux and compiling software.

Archived page from TheFae's github repo

Mudlet - "Fae's Mudlet"

Current Version: 2.1.0-fae8b

Fae's Mudlet is a Fork of Mudlet 2.1 intended to expand IRC and other functionality in Mudlet, mainly for the needs of Botman - A 7 Days To Die Server Manager.
This branch is the active development branch, it has the latest custom code stuff and may be unstable at times.

The code here has been tested with Debian 8.5, Ubuntu 14.04, and 16.04.
These commands should get most Debian-based users up and running:

NOTE:  The 2 links below no longer work but their contents is in the zip at the top of this page.

wget https://raw.githubusercontent.com/itsTheFae/FaesMudlet2/master/setup-debian.sh
chmod +x ./setup-debian.sh && ./setup-debian.sh
wget https://raw.githubusercontent.com/itsTheFae/FaesMudlet2/master/build-mudlet.sh
chmod +x ./build-mudlet.sh && ./build-mudlet.sh

In order to run the build after it finishes compiling you must always use the run-mudlet.sh script. A direct path to this script will be printed by the build script. The run-mudlet.sh script can optionally be passed a combination of flags defined as follows:

    -h -- Shows Help text.
    -x -- Disables prompting for input but displays output.
    -q -- Disables all prompts and console output. Can be used with '-d' option.
    -d -- Enables logging output to a file, used for debug and support.
    -r -- Waits for the process to close and then restarts Mudlet. WARNING -r will require a forced quit or Ctrl+C to stop !!
    -s -- Causes the script to sleep for 1 second when starting.
    -s [#] -- Causes the script to sleep for a number of specified seconds when starting.

The scripts provided here will not run the make install commands by default. The 'make install' commands are not (currently) supported or tested by me and may cause issues with previous or future installations of Mudlet from more official sources or package manager distributions.
Compatibility Differences

    Lua Function sendIrc() now returns 1 on successful send or 0 on errors / not ready for sending. Used to return nil.
    Lua Function reconnect() now accepts three optional arguments, Host (string), Port (integer), and saveToProfile (boolean). Using these arguments will change the connection info for telnet before reconnecting it. If saveToProfile is set to true the changes are saved to the active profile. Example Usage: reconnect('12.34.56.78', 13004, true)

Noteworthy Changes

    IRC Settings are now available in the Profile Preferences/Settings window, and save per-profile.
    The IRC Chat now connects to localhost:6667 until configured by profile settings or Lua function calls.
    The IRC Chat window will not open unless you have loaded a connection profile.
    The IRC client is now started automatically by calls to sendIrc() from lua, unless disabled manually.
    The IRC client will attempt to reconnect to the current connected IRC server if an unexpected disconnection occurs.
    The IRC can be disabled completely by setting the IRC Nickname setting to "DisableMudletIRC" (without " marks.)
    The IRC can also be stopped and started manually by issuing commands /stopirc and /startirc in Mudlet's IRC chat window.
    New Lua functions for interacting with the IRC Client functions and configurations.
    More 'slash' commands supported by the IRC Client.
    New Lua functions for saving and loading window layouts to the active profile.

New IRC Window Commands

    /help - Shows IRC Command help text.
    /join <Channel> - Join a channel.
    /part <Channel> - Leave a channel.
    /listusers [Channel] - Updates the nicklist for the Main channel or the channel specified.
    /listchans - Lists currently Joined channels, including the Main channel.
    /setchan [Channel] - Sets the Main IRC Channel, leaving the previous main channel.
    /joinserver <hostname>[:<port>] - Changes the current server connection settings and reconnects if needed.
    /whois <Nick> - Requests Whois information about given Nick.
    /whowas <Nick> - Requests Whowas information about the given Nick.
    /topic <Channel> [New Topic] - Gets the topic for given Channel, optionally sets Topic on Channel.
    /mode <Target> [New Modes] - Gets the modes of Target (a valid Channel or the IRC Client Nick) and optionally can set modes on Target.
    /oper <User> <Password> - Sends the OPER command to the IRC server using given User and Password credentials. Note: This is a server-wide OPER, not a CHANOP.
    /op <Nick> [Channel] - Grants CHANOP to given Nick in the given Channel. If Channel is omitted the Main channel is used.
    /deop <Nick> [Channel] - Revokes CHANOP from given Nick in the given Channel. If Channel is omitted the Main channel is used.

New Lua Functions

    ircGetHost() - Gets the sessions IRC Host configuration as a string with the format :.
    ircGetNick() - Gets the sessions IRC Nick name configuration as a string.
    ircGetChannel() - Gets the sessions Main IRC Channel configuration as a string.
    ircSetHost( Host, Port ) - Sets the active Host (and optional Port) used for the IRC client. Returns nil.
    ircSetNick( NickName ) - Sets the active IRC NickName. Returns nil.
    ircSetChannel( Channel ) - Sets the Main IRC Channel to send and operate on. Returns nil.
    ircSaveSessionConfigs() - Saves the session IRC configuration to the profile configuration files.
    ircJoin( Channel ) - Attempts to join an additional Channel. Returns int, 1 on assumed success, 0 on local failure. Note: Return value does not indicate actual Join.
    ircPart( Channel ) - Attempts to leave a Channel previously joined, or closes connection if all channels are left. Returns int, 1 on assumed success and 0 on local failure. Note: Return value does not indicate actual Part.
    ircGetChannels() - Returns a string of currently joined channels, delimited by spaces. Returns an empty string when not connected.
    ircGetNicks( Channel ) - Requests the Nick list from the Channel given, activates sysIrcStatusMessage event when the list has been fetched. Returns string, a cached Nick list for the Channel if available or empty string if not.
    ircWhoIs( Nick ) - Requests IRC Whois information for the given Nick. Results are passed back via the sysIrcStatusMessage event.
    ircWhoWas( Nick ) - Requests IRC Whowas information for the given Nick. Results are passed back via the sysIrcStatusMessage event.
    ircOper( User, Password ) - Sends the OPER command to the IRC Server. Results are passed back via the sysIrcStatusMessage event.
    ircOp( Nick, [Channel] ) - Grants CHANOP to given Nick in the given Channel. If Channel is omitted the Main Channel will be used. Note: Requires OPER or CHANOP first.
    ircDeOp( Nick, [Channel]) - Revokes CHANOP from given Nick in the given Channel. If Channel is omitted the Main Channel will be used. Note: Requires OPER or CHANOP first.
    ircIsOper() - Returns a boolean value denoting if the client has successfully been granted OPER on the IRC Server.
    ircIsChanOp( [Channel] ) - Returns a boolean value denoting if the client has been granted CHANOP on the given Channel. If Channel is omitted the default Main IRC channel is used.
    ircMode( Target, [Modes] ) - Will get or set Modes of Target, Target must be a valid Channel name or the current Nick of the IRC Client. Results are passed back via the sysIrcStatusMessage event. Note: Requires OPER or CHANOP first.
    ircTopic( Channel, [Message] ) - Will get or set the Topic message of the given Channel. Results are passed back via the sysIrcStatusMessage event. Note: Requires OPER or CHANOP first.
    ircReconnect() - Will simply and forcefully disconnect the IRC Client and then reconnect using the IRC settings in the active profile. Returns nil.
    saveWindowLayout( [Version] ) - Saves the current window layout to the active profile, Version integer is option and defaults to 0.
    loadWindowLayout( [Version] ) - Loads a window layout from the active profile if it exists, Version integer is optional and defaults to 0.
    saveProfile() - Saves the currently active profile to disk. Unsaved items may not be saved.
    closeMudlet() - Closes the Mudlet application completely, does not save profile data or prompt the user to save it before closing.

New Lua Events

    sysIrcStatusMessage - Event much like sysIrcMessage but for handling IRC Client status updates. This event is only activated when certain functions are called, however the event may fire several times per each function call until a specific IRC Code # is received from the server which ends the event sequence.
    Three string type arguments are passed to this event's handler function:
    -- Subject is usualy a Channel name or Nick name.
    -- Data is usually the text sent back from the IRC Server, re-formatted in some cases.
    -- Code is always a number, indicating the type of IRC message sent from the IRC server.
    The event is activated by the following Lua functions:
        ircGetNicks( Channel ) - Passes the Channel name as Subject, Nick list as Data, and the IRC Code #.
        ircWhoIs( Nick ) - Passes the Nick name as Subject, Whois line as Data, and the IRC Code #.
        ircWhoWas( Nick ) - Passes the Nick name as Subject, Whowas line as Data, and the IRC Code #.
        ircOper( User, Password ) - Passes the client Nick as Subject, the status text as Data, and the IRC Code #.
        ircMode( Target, [Modes] ) - Passes Target back as Subject, the MODE response line as Data, and the IRC Code #.
        ircTopic( Channel, [Message] ) - Passes Channel back as Subject, the Topic query response line as Data and the IRC Code #.