If an english string in a doc uses an entity that is not from global.entities, you *may* either:

1: define a localised version 
	English string says "This is an &english-word;"
	your string would then say e.g. "Det är en &svensk-ord;", and you would have 		
	&svensk-ord; defined in sv/user.entities

2: expand it in place: 
	English string says "This is an &english-word;" 
	your string would say e.g. "Det är en svensk-ord".

Either of these solutions are correct, which you choose is up to you, although i suggest a consistent policy is going to be a lot easier in the long run.