Charset plugin lets you encode or decode data using charsets, with 3 levels: global, by server, or by channel. This plugin is optional, but recommended: if it's not loaded, WeeChat can only read/write UTF-8 data.
Charset plugin should be autoloaded by WeeChat at startup. To be sure plugin is loaded, try: "/charset". If command is not found, then load plugin with command:
/plugin load charset
If plugin is not found, then you should compile again WeeChat with plugins and Charset support.
When Charset plugin starts, it displays terminal and internal charsets. Terminal charset depends on your locale, and internal is UTF-8. For example :
-P- Charset plugin starting, terminal charset: ISO-8859-15 (WeeChat internal: UTF-8)