Maybe this is related: per
https://www.wikidata.org/w/index.php?diff=275935&oldid=275916
the [[links]] do not work on description field.

(In reply to comment #0)

The code "<i>The Man Between</i>" do not show up as italic text in the title of
the item. Changing it to "''The Man Between''" didn't solve the issue:
https://www.wikidata.org/w/index.php?title=Q3092&diff=314190&oldid=249680

We can allow limited tagging in the field, but then we must strip tagging for term search and similar. Some kind of stripping would imply rewriting the string, and this could be quite complex.

The only allowed tags would be <i> and <b>, and only some characters would be legal in <sub> and <sup>.

(In reply to comment #1)

Maybe this is related: per
https://www.wikidata.org/w/index.php?diff=275935&oldid=275916
the [[links]] do not work on description field.

Note the bug 41560.

Also note that labels are used for identifying the entity, so html tags (or other encoding) will break lookup if they are not properly removed before storing to the term cache.

That basically means: Don't add tags and hope it will work as an correct untagged label, it won't without work additional code.

To clarify: at the moment no wikitext or html markup, or any other kind of markup, is supported for labels, descriptions, or anywhere else in a data item. This is by design, and it's unlikely that we'll implement support for wiki markup in general.

If you feel that there are important reasons to allow links (or italics, or whatever), I suggest to make a page somewhere and collect the use cases, so we can discuss what to do about them.

Per design, as Daniel explained.