not always h

 

With four official languages in Switzerland, trying to fit Schweiz, Suisse, Svizerra, and the Romansch Svizra would take up most of the room on a stamp, so they settled on the Latin name 'Helvetia' (official name Confederatio Helvetica- why the CH as the international country code).  Interestingly, in Irish Gaelic and Romanian, the name for Switzerland is closer to Helvetia than variations of Swiss.

'Croatia', on the other hand, is from the Latin name for the country. Hrvatska is derived from the Slavic name, which is used by the people themselves.  The international country code is HR instead of CR because it was already taken by Costa Rica.  I admit, I often initially mistake HR for Hungary

another country with a non English name on their stamp (we'll get to that one with 'M')

I found an interesting article explaining how Croatia/Hrvatska came to be. The original Slavic name was Horvatska, later into Hrvatska.  Latin does not really pronounce the letter 'h', and starting the name with just an 'r' wasn't quite right, so they made it a 'ch' which became just a 'c'.  A 'v' after an 'r' is easy for Slavic speakers but not Latin, so it was transformed into a vowel 'o'.  So now we have a Slavic 'Horvat'  which became Hrvat, which became a Latin 'Croat' with the usual Latin ending for Slavic countries 'ia'