Answer
Some additional mods have their own achievement lists. This button switches between them. Eg, if the button says “Minecraft” it is showing the Vanilla achievement list. If it says, perhaps “IndustrialCraft” (a different mod), it will be showing the IndustrialCraft achievements.
However, because the mods you currently have do not add anything else to the game, this does not have any other unique achievement lists.
Attribution
Source : Link , Question Author : Fennekin , Answer Author : Ben