To write non-integer numbers in the decimal system (without fractions), one needs a decimal mark. In English one uses the decimal point, but in many other languages one uses a comma instead. Wikipedia has a whole article about different decimal marks and where each type is used.
When writing large numbers, it is useful to group digits, typically in groups of three. Conventions vary again: Some would write a million as 1,000,000, some as 1.000.000, others as 1 000 000, and also 1'000'000 is in use.
The decimal and grouping marks typically depend on language. What are these marks for contemporary Latin? Is there any uniform practice or guideline, or is it inconsistent?