There are two different Exchange server editions available:  Standard and Enterprise (see editions comparison). Standard Edition is for small or medium size organizations and limited to 5 mounted databases per server. Enterprise Edition is for large organizations and can scale to 100 mounted databases per server.

A client access license (CAL) is required for each user or device that accesses the server software directly or indirectly. The number of servers used does not matter. 
•    A Device CAL licenses anyone using that device to access Exchange. Device CAL makes the most economical and administrative sense for an organization with many users using one device, such as shift workers who share the same PC to access Exchange.
•    A User CAL licenses a person to access servers running Exchange from any device. If the number of users is fewer than the number of devices, a User CAL is the most economical choice. It also
makes sense for an organization with employees who access the corporate network from multiple devices—for example, from a cell phone or a home computer. 
Two types of User and Device CALs are available: Standard and Enterprise. Which you use depends upon the functionality your business or organization requires. You can have a Standard CAL for either the Standard or Enterprise editions of Exchange. In addition, you may add an Enterprise CAL. Please see the Standard and Enterprise CAL features comparison table.

After license procurement, one can find media for current and previous versions in all available languages on the Microsoft VLSC website. Before purchasing licenses, please carefully read the Exchange Server 2019 Licensing Datasheet.