[On Windows I'm no whiz at all - but this is at work where I can't use anything else]
I'm not using any national layout, just the default US layout. My keyboard is a plain 101-key US keyboard with an AltGr key.
I doubt the problem is in the layout file itself. If I change eg. the "€" character in the layout.ini into a plain ascii character eg. "e", AltGr+5 produces that character correctly. Also if I put the "€" character on a normal or shifted key, it works correctly. Only for non-ASCII characters on AltGr-keys there is a problem, and I have to use Ctrl+AltGr (that is right Alt, Ctrl + Left Alt doesn't work until I enable that option in pkl.ini - so there is "awareness" of the AltGr key).
Also, the problem is there in most apps, but not in eg. my VNC client. Very strange...
I think it's rather a problem in PKL's non-ascii character insertion method... Changing that to "c" (in nonascii.ini) works (copy the character to the clipboard, paste it, then restore previous clipboard contents), but that has other drawbacks.