You can translate StrokeIt by editing the default.lng contained in the Strings directory. You can also translate the plugins by editing the default.lng file contained in each of the directories inside Strings\<PluginName> directory.
When you create a translation, you should save the files as MyLanguage.lng. StrokeIt will automatically detect the available languages. You can switch languages in the preferences.
To simplify translation, you can grab the translation pack.