OpenSSF Best Practices Badges - Internationalization

In order to fully validate the silver level of OpenSSF Best Practices Badges for our project, we have to fully implement internationalization.

Currently messages error are not translated and should be.

Here is the requirement to meet:
The software produced by the project SHOULD be internationalized to enable easy localization for the target audience's culture, region, or language. If internationalization (i18n) does not apply (e.g., the software doesn't generate text intended for end-users and doesn't sort human-readable text), select "not applicable" (N/A).

Here is the questionnaire :
https://bestpractices.coreinfrastructure.org/en/projects/5925?criteria_level=1

[Sander3003]

The OpenSCD core initiative will help with more easy translations; This initiative excludes the error messages translations.

[dlabordus]

For the Backend Services we need to figure out how to do this and how it can be easily passed from the Frontend (OpenSCD) to the backend, maybe using some standardized HTTP Headers.