There are two separate questions: whether the underlying databases are indeed protected by copyright, and whether your product has "substantial similarity" to the database. A database might be a phone book or some other automatically-generated thing, where there is no creativity involved in creating the database, and no copyright protection. It might also be the product of a painstaking process of judgment and data-arrangement based on reading the entire corpus of Ancient Greek, in which case it would be protected by copyright (even though the underlying text material is not protected).
It would likely be found to be infringement, if you were to copy the Greek database and perform a mechanical format conversion. The test that would be applied is, is your product substantially similar in terms of the organization (and not data) to the original? Because of functional requirements, there are only so many ways that a database can be constructed, so some degree of similarity would be logically necessary. This study from the copyright office may be of some use in figuring out where your plan falls, given the target databases.