“Si” with an accent on the i is “yes,” while without the accent, it is “if.”
I can’t type the diacriticals.
I use Duolingo daily on my Android phone. The long press support provides access to the necessary diacriticals. Welsh uses the "caret" and "diaresis". Irish and Scots Gaelic use accent and accent grave on vowels. Do it wrong and the word is incorrect. German uses "diaresis" aka "umlaut". The word "schon" means ready without the umlaut on the "o". Add the umlaut and it becomes "pretty". German has a double S that looks similar to the Greek letter for beta. German uses three letter-diacritic combinations (Ä/ä, Ö/ö, Ü/ü) using the umlaut and one ligature (ß (called Eszett (sz) or scharfes S, sharp s)) which are officially considered distinct letters of the alphabet.
Welsh tosses in some diphthongs treated as single letters for collating in the dictionary. (ch), (dd), (ff), (ll).