Expose used language in a way that allows putting into the data model

### Description

The users preferred language is set on the user profile and will be used when creating a new instance. However this does not necessarily reflect the actual langue being used. If the form isn't available on that language it will default to norwegian bokmål and if the application developer has included the language selector you can override your profile value and select something else.

The profile language is also available as a configurable prefill value. So having some sort of dynamic variable that can be inserted into a field in the data model would solve the problem. Service owners are required to answer in nynorsk if that is the the language the user used or bokmål if thats the language they used. So we need a way to submit the actual language code used, and not try to guess it based on some text input fields.

### Additional Information

This should be solved in a way allows us to extend this concept to include other type of dynamic metadata or texts and values from components that are currently only available in frontend. For example we have the case of the actual text of a radio button/checkbox/dropdown and not only the value.

### Tasks

_No response_

### Acceptance Criterias

_No response_