I'm using EE 2.6.1 and the default language is Dutch. When installing a module it seems that a specific lang file should be added in the language directory. I don't know which modules add lang files. All works fine but when I log out I get an Error when accessing the front-end site. If I'm logged in the front end doesn't show errors.
Right now I make a copy of a lang file en rename it.
Is there something I should adjust with the configuration? Or is there a solution to bypass this when a lang file is missing?