How can I Change the store language after switching the store
You can set Locale as per store view.
Admin >> Store >> Configuration >> Select your store from store drop down on top left corner >> Locale Options >> Set your language for store.
Admin provide to Add Product as well as category data in different language as per store view.
Here for Product : Admin >> Products >> Catalog >> Open Product >> Select store view
Here for category : Admin >> Products >> Category >> Select Category >> Select store view
Note : To convert into different language you must need to install language pack into Magento as per store view.
Create CSV in Below format :
sku | store_view_code | attribute_set_code | name
sample | fr | Default | sample in franch
Add your 1000 products in this format with store_view_code and import products from System >> Import >> Products