With half of Portugal joining, but also because there's plenty of Dutch people here, it would be nice to introduce a language tag.
On the author side, clients should follow the keyboard language setting* and display a little flag in the corner which the user can adjust** if needed.
On the reader side, clients should let users choose between ignoring specific languages***, auto translating or showing a translate button.
Typically when I write in Dutch it's because the context is local and safe to ignore by the rest of the world.
* = or "AI" if you're into that
** = that's about the max effort I'm going to put in signaling the correct language
*** = maybe show a little flag to unfold the message - especially because the tag might be wrong, e.g. I don't always toggle the keyboard
https://github.com/nostr-protocol/nips/tree/master?tab=readme-ov-file#standardized-tags
