>overwhelmingly swiss citizens are against joining the EU

According to a Report from ETH Zurich [0] 16% of swiss citizens support joining the EU, so this confirms your statement.

[0]"Sicherheit 2018", page 21 https://css.ethz.ch/content/dam/ethz/special-interest/gess/c...

> Switzerland would first need to be part of the European Union to be able to be part of the Euro Currency region.

That's incorrect, there are non-EU countries using the Euro too like Andorra.

Andorra has a population of 70,000, you can't use it as an example of what Switzerland could do.

Kosovo and Montenegro (1.7M and 0.7M habitants) are unilaterally using euro. Other (bigger) countries have their money pegged to euro : https://en.wikipedia.org/wiki/International_status_and_usage...

Yes, technically correct statement, but in practice, not gonna happen

> Switzerland would first need to be part of the European Union to be able to be part of the Euro Currency region. They voted against this in 1992 and again in 2001. I am not swiss myself so take this with a grain of salt, but a quick research showed that overwhelmingly swiss citizens are against joining the EU to keep their independence and their unique way of doing democracy (direct votes on issues) probably couldn't work so well anymore.

From a legal perspective, what's stopping any country from adopting the Euro? In theory they could continuously purchase euro with their currency and limit national currency use. Obviously there are downsides to the country doing it but is there anything legally stopping them (in an international law sense)?

Yes, though they have a very close relationship, so they're "out but close enough"