The primitive type "char" represents an element of String in UTF-16 encoding. Technically, it is an unsigned 16-bit integer, and we can do mathematical operations with it. In many languages one letter corresponds to one "char", but letters from some languages (such as Chinese) correspond to sequences of two or three "char"s.
To find out which value corresponds to which letter, look at the Unicode specification. Unicode values between u0000 and u7fff are represented by one "char". For example:
|Unicode number||char||The letter|