A lot of custom chats rely on UserInputService or similar services to detect keypressing on the / (Slash) key.
Although with the mass mixture of games on ROBLOX using default chatting and custom chat systems, it becomes horrendeous for players without an US keyboard. On my keyboard, I can press / just fine on the default ROBLOX chat in-game, but I need to press - (where / is located on US keyboards) when I want to chat using custom chat GUIs.
Now, the difference here is that the ROBLOX chat CoreScript has access to GuiService:AddSpecialKey and GuiService.SpecialKeyPressed. Game developers don’t.
By unlocking GuiService.SpecialKeyPressed, game developers are allowed to give the exact same experience regardless of keyboard setup, making it easier to communicate. It’s either this, or for services/objects such as UIS or PlayerMouse to register / properly.
Examples of keyboard layouts in Europe that has the / key located as a combination of Shift + 7.