Improve language detection accuracy

[ssg]

Problem: when you're typing a post, "are you writing in X language?" prompt appears and disappears occasionally. That frequently happens when you press space and start writing the next word too as the half-word is probably unknown to the model. When you finish the word, the prompt appears again, but this makes the prompt unnecessarily blink, and lose opportunity to notify the user. That can cause posts appear with incorrect language settings and can be quite harmful for its reach (as mentioned in #7260).

This change aims to improve the UX of "are you writing in X language?" by discarding the last word from the detection set until a more reliable detection library replaces lande.