I tried to experiment adding localization files to my airport packages, containing some ATCCOM.AGENT_NAME and ATCCOM.AIRPORT that are not included in stock files. But even with an updated layout.json it doesn't seem to work. Editing default locpak files (in fs-base folder) doesn't work either. I found no word in the SDK about customizing those files and getting the sim to speech the actual airport/city name instead of spelling any ICAO unknown to it.
Can we get some enlightment on that topic in a future SDK update ?