If you search on this in the EL you'll find we've been over this before.
I've rolled my own. I find Smarty great...but just way too much. I could add more features to mine until the end of time, but then why?
Basically, I have two types...system variables and system functions...example...
<plugin:name_of_function <%system_variable%>,<%ID%> />
Nothing fancy. Basically, it will replace all system variables first and then replace any plugins with their code counterparts. Actually, it will replace system variables twice so that users can use them in their content as well.
Your English is very good. 😉
Note: I know that some folks prefer to use straight up PHP for these kinds of things, but I feel that PHP is for developers...users should only be told/taught what they are allowed to use at the content side of things (orrrr, that is my opinion on the subject).