If you use Minecraft with the language "Português (Brasil)" and open the chat, you will see that the first word starts with a small letter, and start a phase with small letter in Portuguese is considered incorrect. Here are some images.
To reproduce this bug, you will need:
1. Set your minecraft language to "Português (Brasil)";
2. Join any world, realm, or anything that you can open the chat in minecraft;
3. Open the chat