Can you test this on 3.8 please

@wilsonge
These 2 errors do not exist in 3.8.
Evidently, if we use the "Modern Browser", the links thereafter (when no hidden menu item for a Root category) will give
joomla-cms-3.8-dev/fr/?view=article&id=2:article-fr-fr
joomla-cms-3.8-dev/fr/?view=category&id=9
until someones codes a fall back to legacy SEF when no root menu item.

There shouldn't be a modern SEF router setting in J4. That only exists in 3.8 - and the results of 3.8 SEF with modern routing enabled should be the same as J4 :/

That is not the matter here. Remains the 2 errors I stated which still exist in present 4.0 branch.

@wilsonge wrong url when home is a featured menu item #18771

This is big Joomla 3,8 url issue and huge problem for real sites

@wilsonge

I tested this again in present 4.0 branch
Solved: Page title is now correct depending on active language menu item.
Not solved: The Home menu items give http://localhost:8888/joomla40/fr/?view=featured instead of http://localhost:8888/joomla40/fr/ when the home is a featured view.

I suggest to test #18429

@csthomas
This Issue is for 4.0.

But will test #18429 on staging as we may have the same issue indeed

In fact that specific issue with ?view=featured does not exist in staging (for Home pages)

Interesting:
#18429 can be applied to the 4.0 branch.
It indeed solves that specific issue with featured menu items as Home pages in multilang but creates other issues
. for example when clicking on the title of an article where the langtag is added at the end of the url
http://localhost:8888/joomla40/cattoutes/categorie-fr-fr/article-fr-fr/fr/
=> 404

EDIT: in fact that issue already exists in 4.0

@infograf768 Are you saying, #18429 fixes issue with featured and does not break above mentioned issue with language?
I yes, can you add a comment at #18429 ?

well, that is in 4.0 and does not solve the article wrong placement of sef lang when clicking article.
as i said, i do not have the home page issue in 3.8 in multilingual

I cannot confirm this. Either it has been resolved elsewhere or ....

Title is now corrected when menu item is Home.

Any link which is not home is broken. Will create issue