Templates are not available in all languages, and we want to communicate these issues to the user (T192271). In addition, we want to provide a default behaviour that is useful and creates the least confusion.
Currently templates in the source article for which a corresponding templates do not exist in the target wiki, are copied verbatim. For example, the 2nd paragraph of Curiosity (rover) from English into Spanish has the [[ https://en.wikipedia.org/wiki/Template:Curiosity_Mission_Timer | Curiosity Mission Timer template ]] (calculating the number in the "2183 sols" text of the example) which is a template only available in English, but it is copied into the translation as "Plantilla:Curiosity Mission Timer". A similar issue happens for the [[ https://en.wikipedia.org/wiki/Template:Time_interval | Time interval template ]] in the same sentence.
# Proposed solution
When an inline template does not have a corresponding template for the target language, it should be added to the translation as rendered text to avoid losing the information.
It will be highlighted a part of the issue card shown for the user to review:
Note that this proposal is only for those cases where we cannot find a corresponding template. If we can find the right template, it will be added to the translation (even if the mapping of all the parameters could not be complete).