If you have problems with chars or accents using Charset plugin:
check that weechat-curses is linked to libncursesw (warning: needed on most distributions but not all) :
ldd /path/to/weechat-curses
check charset line (on server buffer), you should see ISO-XXXXXX or UTF-8 for terminal charset. If you see ANSI_X3.4-1968 or other values, probably your locale is wrong.
setup global decode value, for example:
/setp charset.global.decode = ISO-8859-15