I haven't found any similar existing issue to decided to create a new one. I noticed that `sprintf("%c", string)` doesn't handle (in an expected way) a case when encodings of format sequence and string argument aren't the same and string contains non-ASCII character. In this case it seems to me that `sprintf` uses just binary representation of a character and assigns (or interprets with) encoding of the format sequence string. I would expect that `sprintf` negotiates encoding and converts everything (the character and the format string) to the chosen one. And raise error when negotiation fails. Examples to illustrate this behavior: ```ruby format = "%c".encode("Windows-1251") string = "Й".encode(Encoding::KOI8_U) r = sprintf(format, string) r.encoding # => #<Encoding:Windows-1251> r == "Й".encode("Windows-1251") # => false r.codepoints # =>  string.codepoints # =>  ``` In this example the result's encoding is a format's encoding. But codepoint isn't changed and equals a codepoint of the character in the original string's encoding. But it should be different: ```ruby "Й".encode("Windows-1251").codepoints # =>  ``` Another example: ```ruby string = "À".encode(Encoding::CP1252) sprintf("%c", string) # => in `sprintf': invalid byte sequence in UTF-8 (ArgumentError) ``` In this example the error means that `sprintf` doesn't encode properly a codepoint (of string's encoding) in UTF-8. It uses just raw bytes.