To solve this, you need to add some code to acfields.fdc.

Make a back up of this file ;-)

 First, close Autocad completely.

 This file can be found at (windows 7) C:\Users\xxx\AppData\Roaming\Autodesk\AutoCAD yyy\R19\enu\Support

 You'll have to open it with notepad and search for the following code:

 <FormatType name="Area">

 <Formats>

 <Format>

 <DisplayName resource="471" src="AcFieldRes.dll"/>

 <FormatString/>

 After the second line <Formats> you have to copy-paste the following text:

<Format>

 <DisplayName>Square meters</DisplayName>

 <FormatString>%lu2%pr0%ps[,m2]%ct8[0.001]</FormatString>

 </Format>

Open Autocad again.

Now command field --> Object (field category) --> select object --> format square meters --> OK and place the field

  Good luck

Credits also to Jan vanderborght

Regards