Fabrice Canal from the Microsoft Bing team said on Twitter that "hreflang is indeed a far weaker signal than content-language at Bing," on Twitter. Bing I believe does not really pay much attention to your hreflang markup, as Google does.
In addition, Fabrice added that you should "avoid duplicating URLs just to have them tagged with these language-markets," at least in "most cases" he said. Why? He explaiened that if "you are diluting your links, clicks, impressions and obviously search engines won't index all your content."
In short, he said "less is more." Bing is "able to figure language(s) and markets from links and who is visiting your web sites," he said. For example he said you can "observe that YouTube ranks great (same URL for all languages and markets), Wikipedia content rank great (same URL per language for all markets)."
Here are those tweets:
We are able to figure language(s) and markets from links and who is visiting your web sites. Observe that YouTube ranks great (same URL for all languages and markets), Wikipedia content rank great (same URL per language for all markets). LESS IS MORE.
— Fabrice Canel (@facan) September 10, 2020
More on this from a 2011 Bing blog post.
Forum discussion at Twitter.
