There was one other point that is important to get - master this idea!

The myth of the duplicate content penalty.
A lot of people think that if they have duplicate content that they'll be penalized. In most cases, Google does not penalize sites for accidental duplication. Many, many, many sites have duplicate content.

Google may penalize sites for deliberate or manipulative duplication. For example: auto generated content, link networks or similar tactics designed to be manipulative.

Thanks for the timely posting of this reference. I'm actually days away from rolling out an exact duplicate, in another language, of a site for a bilingual client who serves her clients in 2 languages. Regardless of how Google handled it, it was going forward, but this article provides peace of mind knowing that search engines are treating it as indicated in the article.

Each page of the the 2 versions cross-reference each other in page header tag as follows:

<link href="https://www.example.com/" hreflang="en" rel="alternate" title="English Translation Version" type="text/html" />

I had actually found out about using that tag somewhere else on WW, don't remember who or where but thanks to whoever posted it. The header rel="alternate" is for the search engines and additionally each page also has a visible cross-referenced link for visitors near the main navigation menu.

I'll now consider myself to have been informed ;)

If I had a nickel for every time I had to explain to someone the difference between a penalty and a filter... I'd have a lot of nickels.