Here is an example, with 3 options (and remarks). You can test it with the online validator and adapt it to your detailed requirement.
translate_CtoE.xlsx (12.6 KB).
Would you mind to avoid, please, posting your same issue more than once to the community. It seems even three times, see here and How to shorten a calculation-syntax? and How to shorten the Expression of an Array?.
It is recommended to always test your form with the online validator, during development and before deployment, please.
Could you explain more your requirement? It seems as you might only be looking for an options to get corresponding country codes for a selection. This could be done differently (e.g. using the code as choice name or adding a look-up column or external file). There is also an international standard for country codes, see UN M49 - Wikipedia.
