During the years that I worked for Italian agencies and companies I always noticed that most of the people prefer to read in their native language e ofter ignore or skip content that is in foreign language.
Ofter times website and app offer only one language without the possibility to change it, or worse, they were built without the infrastructure to add more languages.
With the more recent web apps, apps and open-source libraries it's even easier to integrate a system that helps with the content translations. This does not only help your users but also the development and maintenance of the software built.
In my opinion, these are the main pros to integrate a translation system:
The only "problem" is the time used to integrate a translation system, thankfully there are a lot of great open-source libraries online that helps like react-translate (for React).