August's Writing Prompt [Amazing Stories]: Tongue Twister

Yes, it's late for August's writing prompt. It's never too late to talk about writing, though, and with September's writing prompt coming out so soon I thought it'd be a great opportunity to post a double dose of them.

Tongue Twister - originally posted on August 31, 2016

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What if the residents of two countries suddenly switched languages?

Woodland speaks Woodlandian. All its written sources are in Woodlandian, including government documents, archives, reference materials, and even everyday labels like food ingredient labels and street signs. Plainsia speaks Plainsish. All its written sources are in Plainsish, just like Woodland’s are in Woodlandian. One day, every Woodlandian speaker wakes up knowing only Plainsish, and every Plainsish speaker wakes up knowing only Woodlandian. (The few who can speak both languages become poor at both.) No one can read anything unless people from the other country help them.

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Are these countries bordering, close but apart (think like Belgium and Poland having only Germany between them), or on different continents?

Who would star in this world? Translators, second-language teachers, or people whose occupations don't require them to use words very often?

Would these countries grind to a halt, or would they keep going on visual and kinetic clues? Traffic lights still work fine, and watching enough people and your workplace lift blocks implies you should probably also be lifting blocks, after all.

Would their allies help them somehow? Would enemies try to invade?

What happens when a Woodlandian and a Plainsish meet?

The multitude of questions this scenario asks could fill a series.