Message archives (named with the format Msg_XXxx.product.ssarc, where XX is the region code and xx the language code) are Yaz0-compressed SARC archives which contain the game's text files. Multiple different archives exist, one for each language. All of the contents are msbt files.
Contains the names, and other related text, of various actors, including inventory items, NPCs and enemies.
Contains text used in cutscenes.
Contains standard text used in the game's UI, HUD, and menus.
Contains quest-related text, including quest logs and NPC dialogue.
Contains subtitles for voice-acted dialogue spoken by allied NPCs during gameplay.
Contains hint messages displayed on loading screens.
Contains various miscellaneous text, in particular all location names and dungeon names.