If you search far enough back on this site I wrote a very simple example maths processing script language before in C (procedurally). (probably about 6 years ago).
It only had simple add subtract functions, but would work easily.
It's not too terribly difficult to write a scripting language if you're writing the language then you're writing the scripts that run on it. but if you're trying to create something bigger then you have to put in a lot more in the way of error checking!
Certainly a scripting language is easier, BUT, what will your language offer that existing languages don't? (people need a reason to switch).
I like PHP but it does introduce some bad practices.
What bad practices do you believe that PHP introduces?
To be honest I can't think that PHP introduces you to bad practices at all.
it lets you get away with bad practices, (though that would depend on what standard you're trying to write to).
it lets you get away with a sloppy style, (though again, it's your own choice to do that).
a poor workman blames his tools.