Minecraft advancements have internal IDs used to build the advancement tree. Those internal IDs are the filename of the json advancement, and also referenced in the parent field:
"parent": "minecraft:root",

Instead of using display.title, which determines localized strings, DiscordSrv is grabbing the filename only.

DiscordSRV uses the only name available to it. The actual titles of the advancements depend entirely on the client's language settings and aren't even included in the Minecraft server at all.

DiscordSRV should parse the file then, and localize strings as needed to the language configured in DiscordSRV. That's assuming there aren't any hooks for advancements, which there are.

This may have to wait until bukkit updates its API with better advancement support.

This has been implemented for a while