I only did a brief try on the English Wikipedia, but the tool seems to be paternalistic/restrictive to a degree that I cannot find any use for it. It doesn't allow me to write in wikitext (I can only work efficiently in wikitext). It doesn't allow me to use machine translation, although for me it would be quicker to edit machine translated text than to translate from scratch, with the same end quality. Still, it will apparently translate wikilinks, images, and references for me, and that would be a great help. Unfortunately, it doesn't allow me to view the wikitext, nor am I allowed to save the draft to my user account sandbox without having translated everything within the tool (by hand, without seeing wikitext). Do I miss something? Is there a hidden option to view the wikitext at least?
Topic on Talk:Content translation
Not sure how to use this
Thanks for the feedback, @Jens Lallensack. I try to add some details to your different points:
Supporting wikitext editing won't be trivial since the content is annotated for the translation process (e.g., to know which paragraph in the translation corresponds to in the original text). That makes it hard to include that metadata in wikitext without crowding the content, and keeping it in place after content is added or removed.
We are enabling machine translation on different languages gradually. Hearing from community requests will be useful to guide this process. I captured your comment in this ticket.
Saving to user namespace
You can select the "personal draft" option from the publishing settings menu (cog icon next to the "publish" button) to publish under your user namespace. The threshold for publishing is to have less than 99% of unmodified content for the whole document, so a few modifications may be enough to publish. The other warnings shown on a paragraph basis (when unmodified content is higher than 80% for that paragraph) but they do not prevent from publishing (although publishing content will be added to a tracking category for communities to review). We have plans for not applying these restrictions when publishing on the user namespace (more details in this ticket).
Thanks for the detailed answer, this is very helpful!