What I do know, is that the publishing world is very competitive, and fickle. This is just for Americans trying to publish in the USA. When you add the variable of having a Greek book translated into English, it becomes more complex.
My advice is to promote your book, in whatever country you have your book published in. Also, to look for a foreign rights agent willing to take on your book and submit to a traditional publisher. It will take time to find the right agent.
Another option is to hire a translator, then self-publish the book. This will require upfront costs. Alternatives are to translate the book yourself, and self-publish through a company like www.lulu.com who does not charge for publishing.
There are many avenues to take these days in the publishing world and it requires not only talent and creativity, but persistence.