Mouse support has been added to WeeChat, and a "cursor" mode: a mode when you can move cursor everywhere and do actions with keys on focused area.

New commands added:

/mouse
/cursor

Before using mouse, add missing keys:

/key missing

Mouse events (clicks on buttons, gestures) are caught as special "keys", in context "mouse". For a list of default events, you can look at documentation (default keys) or output of this command in WeeChat:

/key list mouse

Mouse is not enabled by default. To enable it (at startup and now), do:

/set weechat.look.mouse on
/mouse enable

When mouse is enabled, you can use shift+selection or shift+buttons to select/paste text (like when mouse is disabled). Note that on some terminals like iTerm, you may have to use alt instead of shift.
New key alt+m will toggle mouse on/off.

Finally, thanks to Nei for his scripts, the mouse support in WeeChat is partially based on them.

Mouse support will be improved in near future, for example interactions with words/messages in chat area (select text, click on URLs, ..).
Stay tuned!