In v10 C# code you typically use something like this:
CMS.Helpers.ResHelper.GetString("LogonForm.Email")
Check out the documentation for resource strings, specifically this:
Resource string priority
When loading resource strings, the system uses the following priority:
- database (Localization application) – highest priority
- site specific resx files
- resx files of custom modules
- custom.resx
- cms.resx
If there are duplicate strings with the same key in all five sources, the system uses the one stored in the database.
So what this means is if there is a key of LogonForm.Email
in the /CMSResoruces/CMS.resx
file, you can simply add that same key in the Localization app with a different value and the system, by default, will return what is in the Localization app (database).