How do you ensure that the company voice & tone comes through in other regions?

Align your culture, the rest will follow. Drink up that company Kool-Aid. :-) 

Then after, ensure the guidelines are practices are evangelized and understood. No one likes to arbitrarily follow rules. Take the time to ensure that the tone, voice, branding is distributed thoughtfully and understood by the regional teams.  

At Spotify, we had clear and strong brand guidelines. We couldn't move out of step of them, and had clear reasons why. It was a brand to be proud of and was treasured. Relay that through your culture and stick to it, and the pride will resonate and become second nature. 

Create and distribute a brand style guide and strategic narrative. Make sure your team is able to give a short pitch, long pitch, demo and is certified on all three. Force Management's Command of the Message framework is a great way to ensure large teams are speaking consistently and presenting value-driven messaging across the customer journey.