In order to separate the performance of individual sites not only statistically but also accountingly, we recommend creating a separate Project for each mutation (site).
Creating a project will create a unique snippet that will be identical for each site.
If the content mutations do not differ by domain but by part of the URL (typically by adding "/cz" or "/en"), the snippets can be run for each mutation separately by parametrically setting them directly in GTM.
If neither option is possible, you can use the same snippet for all mutations, but it is recommended to at least separate the campaigns by language/country abbreviation to track the performance of the campaigns separately.