Hello Pavel,
1) Yes, you are correct. Resource strings can be managed in
Site Manager -> Development -> UI Cultures.
2) You can define resource string for more languages when you click on
All cultures tab and then
New UI culture. This will create a new culture which contains all resource strings of the site and then you can create corresponding translations.
3) If you are referring to resource strings, they can also be edited in CMS Desk -> Administration -> Categories.
4) In default culture, you define resource strings for the default culture and in All cultures tab, you define resource strings translations to other languages. Translating resource strings is described in more details in
Developer's Guide - Translating localization strings.
Best regards,
Filip Ligac