The interface doesn't fit my screen, what do I do?

Take a look at the Factory Planner mod settings (Main Menu→Settings→Mod Settings→Factory Planner) where you'll find a setting for both width and height of the main interface. Turn those down a bit and it should fit your screen.

I noticed a problem with one of the translations, where do I report this?

Translation is mostly handled through a Github project, so opening an issue there is your best bet. If you don't want to use Github, you can also just open a thread here on the mod portal, and I'll pass it along to the relevant translator.