There are languages that Larian does not officially support. For example, the game does not officially have a Korean localization. However, the Korean gaming community is massive. Community translators work tirelessly to create complete Korean language packs. These packs are often distributed via file-sharing sites and torrent platforms, and they must be updated manually every time Larian patches the game.
The "RUNE" designation refers to the specific scene group that released the standalone installer for this version of the game. If you are using the RUNE base game, the language pack is designed to be compatible with its file structure. Baldurs Gate 3 Language Pack v4 1 1 3630146-RUNE
Some versions require you to edit the steam_emu.ini or a similar configuration file. Find the line that says Language=english and change it to your preferred language (e.g., Language=french ). There are languages that Larian does not officially support