Google now recommends using dots for decimal numbers in your review snippet structured data

Dots over commas. Google updated its review snippet structured data help documentation to now recommend using dot separators for decimal ratings. Google added this section twice to the documentation, in both the reviewRating.ratingValue property and the ratingValue property sections.

For decimal numbers, use a dot instead of a comma to specify the value (for example 4.4 instead of 4,4). In Microdata and RDFa, you can use content attributes to override the visible content. That way, you can show the user whatever style convention you want, while also satisfying the dot requirement for structured data.

<span itemprop="ratingValue" content="4.4">4,4</span> stars

Commas still work but not recommend. Google explained that if you are currently using comma separators for decimal ratings in your markup, you’ll still be eligible for review snippets. However, Google now recommends that you update your markup for a more accurate interpretation.

Why we care. If you are currently using commas instead of dots in this application, you may want to schedule some time to update those commas to dots. It doesn’t seem critical but it is something you should add to your to-do list. And if you are thinking about adding this markup to your site in the future, go with dots for decimal points for these review snippets.