"It's also not a great idea to publish your thoughts about names in a web forum."

A very useful point.

First thought on two websites is why? Consider one site with a subfolder in the second language. Easier to manage and more chance of building strength into one domain than two.

The right format will depend on your intentions/target market etc. but for a niche informational site of the type you appear to be suggesting, a .com with a greek language subfolder may work.

You could if you wish geo-target the subfolder to Greece in Google but that's not always best. A site offering real value is perfectly able to rank in different countries and you might wish to serve Greek speakers rather than residents. Again, Google are aware of the language and where that might be relevant to particular searches. If you intend hosting in Greece, for a generic domain such as .com that location will be seen as primarily relevant anyway.

Appreciate the above is a little sketchy but the sort of decisions you are looking at really need a lot more information. A detailed plan of your intentions and the audience you hope to attract.

As mentioned, avoid the underscore, or hyphen come to that. Will cause errors, confusion and Google are perfectly capable of splitting logical words. They will take a little notice of the domain name but not a vast amount by itself. The content and focus of the website are the keys.

One of the reasons domain names appear stronger than is the case is the common use of domain names in link anchor text from other sites e.g. kitchentools .com will often be referenced using "kitchen tools" - "the kitchen tools site" etc. That text helps with ranking, a reason in itself to use a well named domain.

Incidentally, I wouldn't go with the suggestions you put forward. Think more along general lines, including the terms people will use to search for your content. A tool such as click here or click here# will give an idea.

just make our domain name simple