Syntax for multi language site?

Not sure about the required syntax for the routes.yaml file for three or more languages. I understand that in the example on Gost docs, for the main language, the filter is “tag: -de”, and for the German section, the filter is 'tag: de". But how to indicate the main language in case there are 3 languages?

Is that “tag: -de -nl” or “tag: -[de nl]” or “tag: -de, -nl” ?

Thanks,
Robert

I have not tested but you can try this

    filter: 'tag:-de+tag:-nl'

According to this