GrandPerspective is fully internationalized and supports Base Internationalization since May 2016. This means it is now easier to provide translations. You do not have to update the UI anymore in Interface Builder. Instead you can provide all necessary translations in a standard XLIFF file.
If you want to help out with making GrandPerspective available in your mother tongue, or any other language you speak fluently, go to the GrandPerspective Localization forum to express your interest. I will then get back in touch and provide you with the XLIFF file that you can then start translating.
No gotcha's yet for translating the app, but I expect we will discover some as I receive the first translations using the new localization mechanism. We can then also fine-tune the way of working.
If you decide to also translate the help documentation watch out for the following:
Do not translate the content of the AppleTitle meta tag in the main help file. The content of this tag in the GrandPerspectiveHelp.html should be set to "GrandPerspective Help", as the help documentation will otherwise not load in the Help Viewer. The reason is that the content must match the value of CFBundleHelpBookName in the application's Info.plist file (which is not localizable).