Thanks for your question! This is a good one. My colleague, Shayn Smulyan, is currently working on a blog post about this. We hope to publish it in the coming weeks.
We did approve a fee waiver for DOIs registered by the same member that are translations of another DOI (those must be linked with a
isTranslationof relation as documented here: https://0-www-crossref-org.libus.csd.mu.edu/education/content-registration/structural-metadata/relationships/#00044), but the technical implementation of that policy change has not yet been completed, so it will be free in the future (once that implementation has been completed).
Bruna has discussed this on the forum previously: DOIs for Translation/Version
Take a look and let me know if you have any follow-up questions,
Translation of original message:
Hello Bruna / Edilson. Is there any step by step to link the DOI of articles that are in more than one language? I contacted Crossref via e-mail and was informed that it is not possible to assign different DOIs for the same article without additional charges, but in the presentation it was informed that it was possible.