For the initial version of Content Translation (CX1) we provided this kind of editor for templates. When the new version of the tool (CX2) was created that feature was left out. Since the new version was based on Visual Editor, the standard template editor was used, and building a custom one represented a significant effort. We don't have plans to work on this in the near future since our strategy is a bit different:

• Support templates to be transferred automatically. We are applying a machine-learning approach to make sure that most templates can be completely transferred across languages. More details in T221211: Parameters matching on Templates: ML Exploration .
• Support users to map general templates instead of particular instances. When the previous approach fails, users can access a custom tool to define the mapping between the template parameters. In this way, they not only fix the specific template for their translation, but help other instances for such templates to be correctly mapped the next time (for them and others). More details in T221534: Define template parameter mapping between languages as a wiki page.

Improvements in both fronts seem more promising than building and maintaining a custom parallel template editor in Visual Editor for specific instances. In any case, please let us know about specific examples of frequent templates that are not correctly mapped so that we can investigate and use them as examples to improve the support.

Thank you!

I was facing the case of {{cite news}}, on English Wikipedia not being transferred/converted to French Wikipedia. {{Cite news}} used to be used on French Wikipedia, but it has been replaced by {{Article}}. However, Cite news template has been kept for compatibility purposes, and this may explain why I don't have the compatibility I expected.

756 pages are using this obsolete template on French Wikipedia, and I'm pretty sure this could be fixed by the community one for good; a good way to guarantee the compatibility of the template for future usages. However, this would not cover all cases, like T221534 plans to. Can't wait to have this working! :)