For having a language at Visual Studio Ui , basically the language package of that language must be installed during the installation.
You can not select a language in options -> environment -> international settings that didn't installed.
If the language that you want to select in above path is not appearing than you have to modify your visual studio by re-executing installer and selecting Language Packages tab and check your language that you want to have.
And than at Visual Studio toolbar just click Tools --> Options --> Environment --> International Settings and than select your language from dropdown list.