You don’t have to use a language pack that installed. But they are ne neccessary for certain things. For example, some languages have a lot of special characters, for example German. So you have to install the German language pack for those characters. At least the input codes from thee keyboard, as I have it. You also need to install the fonts for said language packs, they go together, as far as I know.
Then you need to make sure your default language is set and your Locale is setup correctly.