Most of the population lives in the flatter parts of Switzerland, which are of no real concern for invasions from the West and North. The linguistic border runs inside Switzerland because the geographic border does as well.

That is a myth. These defenses you talk about were built partly with cheap material and therefore significantly less effective. This caused a major post-war corruption scandal.

Nazi Germany did not invade Switzerland, because Switzerland was actually more useful as a neutral state for Nazi Germany to exchange gold for commodities, for spying and Switzerland produced militiary equipment for Nazi Germany anyway.

Switzerland has also had a policy of armed neutrality since 1815 or before I think and the armed bit would probably be a headache for anyone invading.

The Nazis did plan an invasion. See Operation Tannenbaum[0].

Switzerland didn't end up getting divided between Germany and Italy thanks to the Red Army hurtling more humans west than the Wehrmacht could supply bullets east. Swiss munitions production wouldn't be risked.

[0] https://en.wikipedia.org/wiki/Operation_Tannenbaum

There's this joke in Switzerland: When the war wasn't going so well Hitler sent a note to the Swiss government demanding a supply of tanks. The Swiss council deliberated and responded in due time: "Will one be enough or do you need all six?"