feat: provide an Alternate language content links

[erral]

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Closes #6602

Some comments:

I have found some issues on testing this, because the component injects the links to the Helmet, so I found here that I could use Helmet.peek() to get the current state of the Helmet in the tests and check there the links I inject.

But it had a side-effect: as explained in the linked issue of react-helmet I found that between tests Helmet returns the previous state of the Helmet. So I reordered the tests in order to get them passing. I know that this is not the solution at all, but I haven't found any other test regarding the Helmet in the Volto codebase, so I don't know how to tackle this. Any help will be appreciated.

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[mamico]

LGTM

[pnicolli]

Just to make sure: is this also rendered server-side? In case it's not, do we need it to be rendered server-side?
The code looks good but this kind of things bit us in the past already.

[erral]

Just to make sure: is this also rendered server-side? In case it's not, do we need it to be rendered server-side? The code looks good but this kind of things bit us in the past already.

Er... I need to check this.

[sneridagh]

LGTM, I think it should work on SSR too, but a confirmation would be great.
@erral don't worry about the test, Helmet is basically a hack and has some caveats, but it should be fine.

[davisagli]

@erral Can you check the failing multilingual cypress tests?

[nileshgulia1]

@erral It does work on the SSR but I see this warning in client

Warning: Invalid DOM property `hreflang`. Did you mean `hrefLang`?
    at link
    at head
    at html
    at Html     

if we use hrefLang, I think the browser will handle the conversion. On the server we get it as hrefLang, does it cause issues in SEO ? I think the HTML attributes are case insensitive, the search engines should parse it as hreflang.

[erral]

@erral It does work on the SSR but I see this warning in client

Warning: Invalid DOM property `hreflang`. Did you mean `hrefLang`?
    at link
    at head
    at html
    at Html     

if we use hrefLang, I think the browser will handle the conversion. On the server we get it as hrefLang, does it cause issues in SEO ? I think the HTML attributes are case insensitive, the search engines should parse it as hreflang.

mmmm, this may be something similar to class vs className when rendering the react component.

I need to check this with SSR and the failing tests also, I will tackle this when I have some time later this week.

[davisagli]

@nileshgulia1 @erral HTML attributes are not case sensitive, but in React they are!

[erral]

Just to make sure: is this also rendered server-side? In case it's not, do we need it to be rendered server-side? The code looks good but this kind of things bit us in the past already.

Yes, it is rendered in SSR!