Are the products mostly the same you just have English versions of the meta data and Thai versions of the meta data? If so one feed could work fine you just need to use extra attributes to accommodate the languages. And not all attributes need language versions probably (e.g., inventory, price).
Then you'd create 2 designs, one for the Thai attributes and one for the English. From an activity perspective you could use 2 activities one for each language.
If they product catalogs are unique then 2 feeds would be fine. I'd include an attribute for language/region just to allow easy collection creation. In that case I think definitely want to the 2 separate activities for each language.