Hi,

I've 3 siteaccesses with these locales:

ger-AT@kaiser (frontend 1)
ger-DE@kaiser (frontend 2)
ger-AT@euro (admin interface)

I delete the complete cache (purge).
Access a page at frontend 1, the ger-AT@kaiser cache is generated
Access a page of frontend 2, the ger-DE@kaiser cache is generated
Access other pages of frontend 2 - the cache is taken
But if you call a page of frontend 1, the complete translation cache is regenerated.

The translation cache expires / is regenerated while a page from the other site is called.

Best wishes,
Georg.