but so far can't find anything.
are you sure you were looking for?
if Google can gain from wordpress multilanguage will find a bunch of options.
For example, the WPML plugin, which supports 3 kinds of links - query parameter (?lang=en), subdomains (en.example.com) and any of its subdirectories (example.com/en). In fact, what you want
And there are plenty of other plugins wpml, qtranslate, qtranslate-x, polylang, wpglobus
As well as plugins for translation. pot po mo files. PoEdit (the program) or LocoTranslate (plugin)
Well as useful key words for searching - i18n wordpress, wordpress-l10n, wordpress multilanguage, wordpress translation