Diacritics -- non-English accents

Hi – I deal with items and clients which need non-English language diactitics to accurately display in invoices etc (basically, accents on characters). Sometimes specific items can only be differentiated by a change of diacritic. More often than not, diacritics input into ClearBooks, and display accurately, will output (pdf or print, for instance) as other characters, in particular "?"

In addition, my own address requires the diacritic "ŷ". In my invoice template, where my chosen Google font is sans serif Libre Franklin (set up to import Libre Franklin), the address displays the "ŷ" in a serif font like Times.

How can i set up ClearBooks to sccurately and consistently output the required diacritics?