You are right the version in the Repository is the very basic one for the 505/300 even without topleft icon and without translation.
Lastest version (but I think w/o translation for the string "Calculator") is included in the x.03
download in this thread or in its own thread
here
Please note that the button-actions are realized really quick 'n dirty, and should be redone if the concept proofed working.
There is also the problem of calling compiled PRS+Core function from within sandboxed JS-code. For the Calc I have explicit included the needed code for soGetValue.
Have you already decided how to deal with this - also in regards of the dictionary-code for the 300?