" On the one hand, a language is a means by which a culture symbolizes its identity, binding the members of a social grouping to each other. On the other, the people who do not speak this language are excluded, both because they cannot speak it and because the language will not express their world anyway. Read positively, in the manner of Hamann, Herder's conception means that people are able to explore other worlds by acquiring other languages. Read negatively, it means that one's language can become a factor in a nationalistic exclusion of 'the Other' who does not share one's language.
[...]
At the same time, there is an essential difference between the linguistic nationalism of an oppressed people attempting to assert themselves, and the linguistic nationalism of the kind that played a role in Nazism's attempts to 'purify' the German language of foreign words. Herder himself was thoroughly liberal and progressive, which suggests how complex an issue the relationship of language to national identity can be. Ideas which in one context are thoroughly progressive can, in a different historical context, be anything but progressive. "

― , Introduction to German Philosophy: From Kant to Habermas