In which article?

Oups, forgot to put the link, description modified

Useless span tags around nothing but included inside useless italics: ''<span></span>''

Thanks, filed separately: T113134.

Span tags with lang attributes instead of the correct template to cite text in other language: <span lang="ru">

It's because the source article uses {{Lang-rus}}, which doesn't have a French version. The software cannot adapt a template if it doesn't know how is it called in the target language, and the only way to know it is to have a Wikidata sitelink (a.k.a. interlanguage link).

Templates inside nowiki tags: <nowiki>{{Numéro}}</nowiki>

The translator probably tried to to type wiki syntax, which is not supported in rich text editing. The same would happen in VisualEditor.

Table cells styles displayed instead of being used as styles: ! style="background:{{Communist Party of the Soviet Union/meta/color}}; color:white" | 1

This is T91876.

Span tags with CX attributes: <span class="cx-segment" data-segmentid="539"></span>

I reported T113137 separately. This really shouldn't happen. Thanks for the example.

Language links in the middle of the text instead of a proper link to an other wiki: [[en:Premier of the Soviet Union|Premier ministre de l'Union soviétique]]

As far as I can see, https://en.wikipedia.org/wiki/Premier_of_the_Soviet_Union doesn't have a French version, so it could not be adapted. I'm not sure why did this happen. It could be related to T85932, a fix for which will be deployed next week, and maybe the user inserted it manually, in which case it's not a ContentTranslation issue (it can be done in any editor).

List items ending with br tags: * ... <br>

Already reported as T108169.