You have registered more than one top-level domains (same domain with different tld) but you don't want each of them domain to be simply parked or to just redirect in the main domain.
radio-expert.com (Joomla is installed here, is multi-language site English (default) and Greek)
We would like to use the .com domain to serve the Enlish language and Greek language with .GR domain! SEO result will be better for Greek language viewing the site via a GR domain. This is not rule but I suggest it.
So, a Joomla Multi-language default behaivour is to click on the language switcher module and changes the lanagues
http://radio-expert.com/en or http://radio-expert.com/el
So with the Multi-language Parked Domain Switcher plugin you can convert the links to
IMPORTANT NOTE: All other domains must be "PARKED" in master hosting account, if you have cPanel is very easy to do it.