FYI, there is no need to change GNU ls to get that behavior. You can make it use your locale's separator with either the --block-size="'1" option or by setting the LS_BLOCK_SIZE envvar to that same string:
$ LC_ALL=en_US.UTF8 ls -og --block-size="'1" .
-rw-------. 1 5,145,416 Oct 5 16:44 A
-rw-------. 1 5,137,692 Oct 4 14:37 B
-rw-------. 1 5,147,168 Oct 8 07:52 C
This feature is documented in the "Block size" section of the coreutils manual: i.e., you can type this to see it:
