The Unicode characters are standard. However, encoding them as ASCII strings such as ":lipstick:" is not, and that ASCII string is what goes into the commit me

The Unicode characters are standard. However, encoding them as ASCII strings such as ":lipstick:" is not, and that ASCII string is what goes into the commit message. git will not decode these messages as the emoji characters, as far as I know, and I expect that Linus Torvalds would have some choice words if that were a feature request. Sequences such as ":lipstick:" are a hack to work around the fact that PCs (as opposed to phones and tablets) are bad at both inputting and displaying emoji.