I see many companies that have an international presence trying to localize their social media presence by creating country or language specific accounts. However some seemed to have done so without following a consistent pattern, one example being the World Wildlife Fund when you look at their Twitter accounts:

World_Wildlife : verified account with 200K followers
WWF            : main account with 800K followers
www_uk         : lower case with underscore between WWF and country indicator
WWFCanada      : upper case with country indicator attached to WWF
...

I am planning to build a website which hopefully will grow global and would like to avoid this sort of inconsistencies. Also, I was comparing what Twitter and Facebook allow in their username and found out that they don't allow the same characters to be used (e.g. for instance that the former doesn't allow . whereas the latter does) making difficult to ensure consistency across social networks.

Hence my questions:

Are there known naming schemes for creating localized Twitter and Facebook accounts while maintaining a certain consistency between them (best effort)?

Are there any researches out there that have proven whether some schemes were better than others in terms of readability and/or SEO?