rename the bsz file to .zip
extract it to a folder
edit the skin.ini file:
look for string "Btnx="
where x is 1,2,3 etc
you'll find things like
Code:
Btn1=sambtn1;370,8:10;Play
replace the last part by whatever text you wish (e.g. "Play" --> "Lire")
once you're done, you can either leave this as is (I mean all the skin files in the folder) or recompress as a zip then rename the zip file to .bsz