Does this platform support RTL languages?

Does the templates support Hebrew?

Depends on the template. You can ask in the comments section of a template you are interested in.

Can I check before I purchase a monthly subscription? Does this platform allow trial period of any kind?

No, there is no trial period. If you are interested you can subscribe monthly plan or anual plan.
You can try to search here, hope you will get rtl template (web template/cms/wordpress) here: