Ok, maybe I just don't get it, but what do you mean exactly, how can I reproduce it? :]

Sounds like it should be Wikibase's responsibility. TitleWidget doesn't
ask for a specific language, as far as I can see.

In T125763#1999694, @Florian wrote:

Ok, maybe I just don't get it, but what do you mean exactly, how can I reproduce it? :]

Load VE on a WMF production wiki with your userlang set to en-gb and search for something that has a description in en but not en-gb (in quick testing, Wikia is in this sate right now). You'll get no description. Change interface language to en and you'll get it.

In T125763#2000364, @matmarex wrote:

Sounds like it should be Wikibase's responsibility. TitleWidget doesn't
ask for a specific language, as far as I can see.

OK, re-titling slightly.

Re-titling more boldly. :)

Duplicate of T115122: PageTerms Api Module should support language fallback, I believe?

What makes this non-trivial to fix is that the current API response is:

{
    "batchcomplete": "",
    "query": {
        "pages": {
            "10346388": {
                "pageid": 10346388,
                "ns": 0,
                "title": "Wikia Search",
                "terms": {
                    "label": [
                        "Wikia Search"
                    ],
                    "description": [
                        "defunct free and open-source web search engine by Wikia"
                    ]
                }
            }
        }
    }
}

If we want to add language fallback, then we have to somehow indicate the language that we're returning. And we may have to do that on a per-term basis, as the label might have a match in the requested language, but the description might not and thus is falling back.
All that is doable, but not quick.