Many of your library signs will be in English (or whatever is the main language spoken where your library is).
It may be really important to have signs in languages other than English so that the information reaches the target client group.
This serves a few purposes. It lets people know you have services they may be interested in, in their first language. It also lets people know that you are interested in providing a service in another language and tells the community this.
This sign was in a library where the first language of much of the community is English, however, there are also many people for whom Spanish is their first language.