The short name of buffers can be changed with /buffer set short_name <new_name> command. This might be useful for long channel names displayed in the buffers bar (buflist plugin with WeeChat ≥ 1.8 or script buffers.pl with an older version).

For example on channel #weechat:

/buffer set short_name #wee

New value is used immediately, but is not saved in config file. To make it persistent, you have to use script buffer_autoset.py:

/autosetbuffer add irc.freenode.#weechat short_name #wee

Note1: it's not recommended to set short name of query buffers, because WeeChat will change name of buffer when nick changes.

Note2: you should use command /buffer set with precautions, it is not recommended to change other buffer properties if you're not sure about what you do. This could lead to weird behaviour or a crash.