It does matter depending on how you define your identity, though I think language is not the culprit here. I was in three European countries this year and they all had MTV teenagers but none of the countries spoke English! Football hooliganism at local matches and then at international matches shows that 'pack mentality' is all about our need to define ourselves as part of one group and seperate from another, but that can be at such a small level as between housing estates and as big as continents, the language is irrelevant when defining 'us and them' but its often used erronously to do that.

Sentimentalising old customs, traditions and languages/accents is more about what defines 'us and them' breaking down, and the sense of belonging thats lost, than it is about any of the customs or accents that have gone.