A multilingual project. Each language corresponds to a subdomain, and there are special subdomains for static and special versions (like the Wikipedia):
en.example.com
ru.example.com
...
static.example.com
m.example.com
fb.example.com
vk.example.com
...
Users during operation will accumulate the data that is in principle not necessary on the server side, plus these data can be larger than 4 KB ie cookies use is not desirable.
HTML 5 localStorage, a seemingly perfect fit, but there is one big "but": the data stored for a single subdomain are not visible on all the other subdomains according to the specification of security concerns.
Could you, dear harrowdale, to recommend how to implement local data storage in this case? Did anyone else with a similar problem, successfully solving it? Maybe is any way to use iFrame to store the localStorage there and "chat" with him? Are there any other approaches to solving this problem?