Just grabbed 17w48a for testing and noticed Brigadier now suggests coordinates when you need them. Problem is either:

• Brigadier suggests badly syntaxed coordinates.
  or
• Game expects dots instead of commas for coordinates

What I expected to happen was...:

After reading Brigadier suggesting me coordinates as yellow text and pressing TAB to auto-complete the command, I expected those coordinates to be valid.

What actually happened was...:

After auto-completing, the coordinates were colored red and Brigadier pointed an error. Coordinates were considered valid after replacing commas with dots.

Steps to Reproduce:

1. ► I typed /execute offset in chat, result was Brigadier suggesting attachment 1.
2. ► Pressing tab colored the coordinates in red as per attachment 2, Brigadier pointing to a "Incomplete expected Coordinates" error.
3. ► I attempted replacing commas in the auto-completed coordinates with dots (attachment 3); Brigadier accepted the coordinates.