@candle Only one accent per letter?
You mean like only é, ī, à, ö, but not ê, ì, å, õ?
Or like é, è, ē, ë, but not ë́ or ė̄?

The former should work just fine if you have composition set up correctly.
I'm not sure the latter would work with composition, since you're not entering a single character but a letter followed by two or more combining accents.