China and Japan were both rife with incompatible dialects for a long time. Japan fixed this using a ruthless campaign that basically analogized non-eastern dialect speakers as hillbillies and through standardized education abd media. China did some of that. Both did language reforms.

The US also has a program like this, albeit much softer and mostly generational.

India is a massively polyglot nation that has used a program of education and incentives to maintain and grow English.

The fact that Europe has not nominated a cross-EU language and taken action to move toward linguistic unity is actually an outlier. Note that I’m not saying that this would be a good thing but it certainly would have upsides.