I use a mac (macOS 10.14.4) and encounter a problem after entering a special character on the Mac-way (keep a character pressed and wait for the pop-up). After selecting the special character from the pop-up, the keyboard becomes unresponsive. This happens in all input fields of the UI of jAlbum and only in jAlbum. All other open application work normally. JAlbum must be stopped (Quit by using the mouse) en restarted to use the keyboard again. Even switching the keyboard off and reconnect it again does not help.
I see the same thing on my Macbook. The keyboard becomes unresponsive after trying to enter a special character. I can still click on things, like the OK button to close the settings panel, but that's all I can do. The keyboard remains dead until a close and restart of jAlbum.
I've stumbled on at least one weird little workaround. Once the keyboard locks up, enter CTRL-Space. That frees up the keyboard again. I have no idea why, or whether some other combo will do the same thing!
Thanks for reporting and thanks for the workaround. This is a Java issue, i.e. some interaction bug between Java and OS X. I can reproduce it and report that it's gone in Java 12, but we're currently having difficulties launching jAlbum on Java 12 using the ordinary .app package's launcher so I can't promise when we'll have it resolved.