Smaller countries are far less likely to suffer from secessionist or identitarian agitations, especially small and wealthy countries like Switzerland. Comparison to Switzerland and similar countries is not instructive.
This is especially true for language. Linguistic division within countries is often a source of tension, even in smaller countries. In larger countries, it is almost assuredly going to lead to tension, especially so during times of hardship. This is why the United States must remain an English speaking country. Major regional linguistic differences would quickly fuel secessionist energy in the US, given how much diversity already exists even with relative linguistic homogeneity.
Just to harp on the language point a bit more: language is the soil in which culture grows, and a unified culture is critical for any functioning entity, whether that be a family, a corporation, a club, or a country.