In the UK we use a period for a decimal marker: 12.7

We optionally use a comma for the thousand separator: 4,926

In other parts of the world, for instance mainland Europe, these two are switched to give 12,7 and 4.926

I believe that this second system is confusing (and not just because I'm not used to it) but destroys the clarity of the numbers and surely negatively affects communication.

1.1,1.2,1.3,...,1.9

Vs

1,1,1,2,1,3,...,1,9

You could say the same about using the comma for the thousands marker however that is completely optional whereas the decimal marker isn't. Sometimes having issues with the optional is better than with the mandatory.

I've read the wiki page on this topic and it baffles me that the UK got close to using the comma-for-decimal system.