Do speakers of these languages tend to code switch, or mix both languages in the same sentence?

Question

Bilingual Dutch/German speakers

Trilingual Swedish/Danish/Norwegian speakers

I'm asking because I know a Brazilian lady who also speaks Spanish. Sometimes she uses pronouns from Spanish in her Portuguese conversations. Not a lot, but frequent enough for the trained ear to discern that she is mixing languages.

Answer 1

the native speakers I know in the Scandinavian languages generally keep the forms separate. Very few speakers are true trilinguals, however, usually stronger in one of the three.

Answer 2

The difference between Swedish and Norwegian is rather small, they can almost be viewed as dialects of a common language.

Danish is also quite similar, at least in writing.

For a person who doesn't speak any of these languages I guess they can be somewhat difficult to separate from each other.

Swedish and Norwegians understand each other to a very high degree, although some words may be similar but have different meanings (e.g."rolig" = "fun" in Swedish but "calm" in Norwegian).

In my experience the Danes are often better to understand Swedish than Swedish people understands Danish.

I also think they might speak extra slow and/or use some Swedish words when they speak with Swedish people.

Answer 3

When you are fluent in multiple  languages - it doesn't matter what the combination is - it's often easier to recall a specific word or phrase in one language or the other.  

If you speak to children who are brought up in a multi-lingual environment, they haven't quite learned how to keep their languages separate - they simply mix the words together, switching between languages as they see fit.  This is especially easy to do since all languages contain specific words or phrases that don't exist in other languages, which makes it harder to stick in a single language.