Data register import is just the name of the data register. Values inside the data register is a separate import.
Data registers are used for predefined selection criteria. To import "Data register" names you need to download the import template first, or export Data registers from feed.
The template supports import to the languages you have defined in feed, so when you click on download template you need to select the languages you want to use when updating or creating new "Data registers".
Make sure you create new values on all languages so that users on different languages setting than yourself will see the value in their language as well. This is also important if you will be using these in integrations
Blank on a language will result in blank value for that language.
If you just "update", you can update only on the languages that are missing values on.
You need to specify a import code when importing Data registers.
To see the import codes that are in use on "Data register", go to "Basic data". Under Product, click on "Data register". Here you will se a list of "Data registers" (you can also export this list if needed).
Blank on import code are manually created Data registers that has not received an import code on creation. These cannot be updated in an Excel import (unless they are given an import code first).