eselect, eselect-{repository,locale}: add page (#13228)

* eselect: add page

* eselect-repository: add page

* eselect-locale: add page

pages/linux/eselect-locale.md

@@ -0,0 +1,16 @@
+# eselect locale
+
+> An `eselect` module for managing the `LANG` environment variable, which sets the system language.
+> More information: <https://wiki.gentoo.org/wiki/Eselect#Locale>.
+
+- List available locales:
+
+`eselect locale list`
+
+- Set the `LANG` environment variable in `/etc/profile.env` by name or index from the `list` command:
+
+`eselect locale set {{name|index}}`
+
+- Display the value of `LANG` in `/etc/profile.env`:
+
+`eselect locale show`