sudo apt-get install build-essential automake checkinstall
sudo apt-get build-dep weechat
wget http://www.weechat.org/files/src/weechat-0.4.3.tar.gz
tar zxvf weechat-0.4.3.tar.gz
cd weechat-0.4.3
mkdir build
cd build
cmake ..
make
sudo make install
cd weechat-0.4.3
mkdir build
cd build
cmake .. -DPREFIX=/path/to/directory
make
make install
(use sudo if necessary to install, after compiling)
WeeChat User Docs
http://weechat.org/files/doc/stable/weechat_user.en.html#compile_with_cmake
Ubuntu Docs: Compiling Software
Thanks for this very useful guide :)
EDIT : just noticed there was a ARM-HF .deb package on their download page : here
(It's for raspbian, but I think it should work on ubuntu too ^^)