Inform doesn’t do any in-line code checking or auto-completion. When I’m working with an IDE like that, I often do create acronyms or short mnemonics for often used phrases and then just do a blanket Find-and-Replace before compiling it.
There’s no documented way to do this. (You could write a script to preprocess your source code and pass it to the I7 compiler, but you can’t do this in the IDE.)
It’s possible that the source-language system will eventually allow this. That is, Inform currently uses English language forms, but there are supposed to be ways to adapt this to other languages. You could then build “English-Plus” that adds some of your abbrevations.
But it’s also possible that it won’t work the way you want. Your “isi” is a verb and half of a relation phrase, and there may not be a way to package that up in a single “word”.
To say i: say "[italic type]".
To say b: say "[bold type]".
to say f: say "[fixed letter spacing]".
to say v: say "[variable letter spacing]".
to say p: say "[paragraph break]".
to say l: say "[line break]".
to say /: say "[roman type]".
The “to say” only works within quotation marks though.
With this I can write
say "'Don't shout at me in [i]italics[/],' she hollered back."