[Sukram21]

The Eszett (ß) has been already standardized for several decades (since 1986: with ISO 8859-1 aka latin-1).

The newly added letter is the "capital letter Eszett", which did not exist until recently. One could argue that this new letter is not really needed, as Eszett does not appear in capitalized form except when a word is in all-caps, and was then simply written as "SS".

[jeltz]

The capital version has existed in uncommon use since the early 1900s.

[fanf2]

Standardisation was earlier than that :-) ISO-646 is the 7-bit predecessor to the 8-bit ISO-8859. It dates back to the late 1960s. Like 8859, 646 has several variants, such as ISO-646-DE which has ß where ~ is in ascii. (The trigraphs in C are partly to work around transcoding issues between ISO-646 and EBCDIC variants.)

[tasogare]

Thanks for info, I didn't know that.