IIRC in the early 1900s, coercive methods were used to stop children speaking their native regional languages, a lot of it in school.
In my region of Brittany (France) the most famous example that was on posters detailing good manners would say : "Il est interdit de parler breton et de cracher par terre" meaning "It's forbidden to speak Breton and to spit on the ground", placing both on the same level.
Stamping out minority languages and dialects was (and often still is) unfortunately common in most countries. I'm Russian, and my native regional dialect has some minor differences from standard Russian that make it sound a bit more like Belarusian. I remember how in school we had a teacher making fun of our manner of pronouncing words as "kolkhoznik speech" (implying that only the uneducated speak like that). This was in 1990s.
In my region of Brittany (France) the most famous example that was on posters detailing good manners would say : "Il est interdit de parler breton et de cracher par terre" meaning "It's forbidden to speak Breton and to spit on the ground", placing both on the same level.