This software is open-source and can be found on GitHub. Tank Icon Maker is written in C#, for .NET Framework 4.5.
The ideal way to contribute is to fork the repository on GitHub and submit a pull request. If you wish to make major changes, you might wish to get in touch first, to confirm that they will be accepted.
It's pretty easy to start translating Tank Icon Maker into your language. The menu to create a new translation is right there in the language switcher. Try it! To contribute your translation, just create a new issue and we'll make sure to include it.
Please keep in mind that I no longer have much time to spend on Tank Icon Maker. If you wish the project to move forward, you have to be the one to take it there!