I SUPPOSE that External Keyboard Helper might help with national letters, some kind of Alt + letter = needed character, but the actual number of keys is limited, and if you started also combining Alt + Ctrl + letter = something, you'd need a schematic before muscle memory set in 🙂
Indeed, odd mappings for national letters are just horrible. I struggled with that on e.g. the BB Priv.
And not talking the print here, but we really need at the least 11 columns to get room for one key right of P and two right of L for many layouts.