I still don't get it.
I need CB Registration page and CB Login page visible in all menus for all languages.

1) For menu items with CB Registration page - do I need to make a copy of this menu item for each language? If I do so, I can make language associations and alternate and hreflang will appear in the code, as needed. If not (if I use one CB Registration page for all languages), then there would not be any alternate and hreflang in code - that's bad, no?

2) For CB Login - i've tried to use only this menu item for all languages, it was bad:
- no alternate and hreflang in code
- the title CB Login isn't translated , only content is translated

3) Maybe there is a tutorial for all of this?

Then create menu items and modules with language set to all.

But in this case (if I set CB Registration menu item language to ALL) it would be impossible to translate the menu item titles. (The "Registration" text in english menu would also be "Registration" in russian, but it needs to be "Регистрация")

then there would not be any alternate and hreflang in code

What about this?

2) For CB Login - i've tried to use only this menu item for all languages, it was bad:
- no alternate and hreflang in code
- the title CB Login isn't translated , only content is translated

And this?

docs.joomla.org/J3.x:Setup_a_Multilingual_Site

In this tutorial they make a copy of each element for each language...


Google says:

It's a good idea to provide a generic URL for geographically unspecified users if you have several alternate URLs targeted at users with the same language, but in different locales. For example, you may have specific URLs for English speakers in Ireland (en-ie), Canada (en-ca), and Australia (en-au), but want all other English speakers to see your generic English (en) page, and everyone else to see the homepage. In this case you should specify the generic English-language (en) page for searchers in, say, the UK. You can annotate this cluster of pages using a Sitemap file or using HTML link tags like this:

<link rel="alternate" href="http://example.com/en-ie" hreflang="en-ie" />
<link rel="alternate" href="http://example.com/en-ca" hreflang="en-ca" />
<link rel="alternate" href="http://example.com/en-au" hreflang="en-au" />
<link rel="alternate" href="http://example.com/en" hreflang="en" />

I suppose this means the only possible way to do so, is to create duplicates of menu items even for CB lists, modules, etc.....
(This is written here about hreflang: support.google.com/webmasters/answer/189077?hl=en )
And also as I stated it in this post: www.joomlapolis.com/forum/146-general/237010-solved-multilanguage-cb-where-are-the-alternate-and-hreflang

Correct.

I think there was some kind of misunderstandig... Because when you said:

Then create menu items and modules with language set to all.

and

you do not need to make copies unless you want to. In the case of menu items you would make copies if you want the menu alias to also be multilingual.

I thought there was a way without duplicating menu items.

So as a conclusion:

I suppose this means the only possible way to do so, is to create duplicates of menu items even for CB lists, modules, etc.....