If it is nearly impossible to switch the US from imperial to metric, I cannot imagine what it would take to unify a massive population under a single dialect. I think the answer is measured in generations.
https://en.wikipedia.org/wiki/Anglicisation
Ask French how they've managed to (almost) eradicate the Occitan and Breton and spread the Parisian dialect as the offical variant of French language throughout the country.
They use their own unique set of units that are different to both Imperial and Metric.