I suppose Foroyse is an example of a language
that is different from other languages, and yet,
the Foroyans had neither navy nor army. (But the
Danish king had; Danish nearly took over too,
but som idealists saved the language, by creating
a norm for writing it)
Saami language is another such example. It still
lives.
To my way of thinking the two ideas of tradition and
independence are important for a language to be a
language in its own right, and not just a dialect that
depends on some other, more influential, language
for its maintenance and development.
BTW, I also found the reference I was looking for,
quite by chance, that in part gives an answer towards
determining the independence of the Scandinavian group
of languages from other Germanic languages, and it has
to do with the vocabulary of the Scandinavian or Nordic
languages. Viz. :
"30% av ordtilfanget i nordiske språk finnes ikke
andre germanske språk".
{ Thirty percent of the vocabulary of Nordic languages
does not xist in other Germanic languages. }