You could replace them if you want, but I wouldnt even try.
Those are the language variables which give Xcart the Multilingual capacity it has.
Enter your admin panel, where it says Languages, there you can modify these variables with ease and even modify or add other languages.
There are 4 kinds of varialbes:
- Labels
- Texts
- Errors
- Email
the identifier normally starts with {$lng.lbl_thisandthat}, which means:
1. $lng = the language the user is currently using
2. lbl = the kind of variable (in this case label), used to differenciate them
3. thisandthat = the direct reference to where it is located in the TPL files