>When they don't serve a purpose anymore, they should be replaced by something more functional.
If and when that's a voluntary and organic process, sure. The problem is that replacement more often that not comes about through ethnic cleansing and violence. These indigenous languages were perfectly functional to the people who spoke them at the time but they were replaced because they didn't serve the purpose of colonizers.
And "lost" languages do get reclaimed from time to time. Hebrew and Irish being two examples.
Hebrew was brought back from the dead for the Jewish refugees populating Israel to have a common language. This solved a genuine practical problem.
Teaching Irish to kids who all speak English does not help anyone communicate better. It seems like a nationalist pride project, and those are not my favorite.
Israelis could just as well have chosen English for a common language, or Arabic, or any other living language. Reviving Hebrew was just as much about nationalist pride (or preserving culture if you like) as reviving Irish was for Ireland.
If and when that's a voluntary and organic process, sure. The problem is that replacement more often that not comes about through ethnic cleansing and violence. These indigenous languages were perfectly functional to the people who spoke them at the time but they were replaced because they didn't serve the purpose of colonizers.
And "lost" languages do get reclaimed from time to time. Hebrew and Irish being two examples.