frankly, I don’t care , but it works. maybe it is actually redundant and
is sufficient. quick to make work, anyways. if I remember right, the short version with 1 VARIABLE only leaves over some native-lingo stuff and the long ver. will make it completely english-only for some odd reason.
LANG is the standard default setting for all locale categories, it can be overridden with LC_XXX for individual categories XXX. LANGUAGE is a GNU gettext extension which makes it possible to have an order of priority among languages you want for messages category specifically (LC_MESSAGES). See man 7 locale for further details.
In most cases where you want just one language, and for messages fall back to the built-in default (English in practice) when the language is not available, there is no need to set LANGUAGE.