French set to replace English as EU’s ‘working language’

Neither Switzerland nor Britain have ever reneged on anything. The problem is the exact opposite: Brussels has been changing, in big and important ways. The nature of the EU is that less and less is subject to veto over time, and the EU institutions never cared much what the treaties said anyway. Thus the "rules", such as they are, are constantly changing and often in ways that nobody agreed to.

Indeed the whole blowup with Switzerland is due exactly to that: the EU wants to keep changing the rules without getting the Swiss to agree and has been trying to force them to drop the previous separate bilateral agreements in favour of "dynamic alignment" i.e. accepting whatever the EU changes the rules to be at any time, without any pesky referendums.

And in the UK, a constant source of frustration in London is due to the impression that the UK argues against bad rules when they're being proposed but when passed it follows them, whereas other EU countries agree with the rules (easy) and then ignore them when they are inconvenient. See: Germany deciding that EU law isn't actually superior over their constitutional law, despite that being a supposedly inviolable aspect of EU membership. It's easy to find people who voted to stay in the EU (or EC as it was then), in the original Brexit referendum in the 70s, but who voted to leave in the 2016 referendum with a justification of "this isn't what I voted for back then, I was misled". The EU changed the rules of the game but people weren't consulted until much, much later.