Translation:The relations between Sweden and Finland are good.
Can't we say "the relationships" too? It was rejected. I understand that in this context, "relations" are typically used, but that doesn't rule out saying "relationships", right? Countries can have either "relations" or "relationships," depending on the speaker's point, I think
You can't use the plural "relationships" in this sentence because there are only two parties involved (the two countries). You would have to use the singular "relationship."
To use "relationships," you would have to be talking about at least 3 countries: The relationships between Sweden, Finland, and Norway are good.