The bug

The debug pie chart uses the OS locale specific number formatting, for example for German this means a comma (,) is used to separate the integer part of a number from the decimal part.

How to reproduce

1. Change the locale setting in your OS to for example German
2. Open Minecraft
3. Display the debug pie chart by pressing SHIFT + F3

Code analysis

Based on 1.12.2 decompiled using MCP 9.40

A java.text.DecimalFormat object using the default locale is assigned to net.minecraft.client.Minecraft.displayDebugInfo(long).decimalformat.