Change Language of Lodgit Desk
Normally, Lodgit Desk is displayed in the language selected as the system language on your computer, i.e. in German or Spanish, if this is your default language, and in English for any other language.
In Lodgit Desk, however, you can work in German, Spanish, or English, regardless of your system language.
Mac
You can use the Language Switcher app to change the language of selected programs. Once you have opened the app, select Lodgit Desk and then select German, Spanish or English, depending on which language you want to work in Lodgit Desk.

Windows 10
Under Windows 10, the language in which Lodgit Desk is displayed depends on the language of the operating system - the ability to set different languages for the windows of different programs seems to have been removed by an update.
You can change the language of your Windows 10 installation by following these instructions.