have you installed the multingual sample data through the module?
which precise url gives this result?

I install the new language and content language by the administration after I use the “Install Multilingual” with every notes of success + Multilingual Status OK.

What is weird I even verified that both menu items are pointing to the right (french/English) Category Blog and both article are in their right specific category. I think I will reinstall from scratch to see if I can repeat the problem.

The site is on my local Mamp.

Ok I just reinstall the full Alpha 8 everything work well but see these 2 screenshot something is up?

When French is default
The english page have a french title and no article — The french page is ok

When English is default
The french page have an english title and no article — The english page is ok

Will test with a clean install once #24300 is solved

I confirm.

The issue is with the router.

I am modifying the title of this Issue

This can be tested again on a 4.0-dev branch clean install.
Looks like it works fine for a monolingual site

Hint: the issue is only when SEF is on.

@SharkyKZ
could this be due to one of your prs merged recently?

@infograf768 this has to do with Language Filter plugin changes in 3.9. See https://github.com/joomla/joomla-cms/pull/24192/files#diff-9a4ee24a09bcef172864692ed05135ca.

@SharkyKZ
it works fine in 3.9 and was working fine 3 days ago for 4.0
therefore, something has been modified in the last days that broke it.

sorry, i now understand that some changes from 3.9 have been recently merged by @wilsonge in 4.0

I confirm, i had a Joomla 4 multilanguage website working since months, once installed the latest Alpha 8 all pages throw a 404. Disabling the multilanguage filter plugin fixes the problem, so it must be something merged in recent days about multilanguage.

The issue is in the modification of the onAfterInitialise() method.
It was

	public function onAfterInitialise()
	{
		$this->app->item_associations = $this->params->get('item_associations', 0);

		if ($this->app->isClient('site'))
		{
			$router = $this->app->getRouter();
			// Attach build rules for language SEF.
			$router->attachBuildRule(array($this, 'preprocessBuildRule'), Router::PROCESS_BEFORE);
			$router->attachBuildRule(array($this, 'buildRule'), Router::PROCESS_BEFORE);
			if ($this->mode_sef)
			{
				$router->attachBuildRule(array($this, 'postprocessSEFBuildRule'), Router::PROCESS_AFTER);
			}
			else
			{
				$router->attachBuildRule(array($this, 'postprocessNonSEFBuildRule'), Router::PROCESS_AFTER);
			}
			// Attach parse rules for language SEF.
			$router->attachParseRule(array($this, 'parseRule'), Router::PROCESS_BEFORE);
		}
	}

it is now

	public function onAfterInitialise()
	{
		$this->app->item_associations = $this->params->get('item_associations', 0);

		// We need to make sure we are always using the site router, even if the language plugin is executed in admin app.
		$router = CMSApplication::getInstance('site')->getRouter('site');

		// Attach build rules for language SEF.
		$router->attachBuildRule(array($this, 'preprocessBuildRule'), Router::PROCESS_BEFORE);
		$router->attachBuildRule(array($this, 'buildRule'), Router::PROCESS_BEFORE);

		if ($this->mode_sef)
		{
			$router->attachBuildRule(array($this, 'postprocessSEFBuildRule'), Router::PROCESS_AFTER);
		}
		else
		{
			$router->attachBuildRule(array($this, 'postprocessNonSEFBuildRule'), Router::PROCESS_AFTER);
		}

		// Attach parse rules for language SEF.
		$router->attachParseRule(array($this, 'parseRule'), Router::PROCESS_DURING);
	}

This last one works fine in 3.9 but breaks 4.0

Thanks for the clarification @infograf768 ... waiting for someone more expert to fix it

I confirm that the previous version of onAfterInitialise solves the problem with multilanguage on J4 Apha 8

Using Router::PROCESS_BEFORE instead of Router::PROCESS_DURING here appears to fix the issue.

$router->attachParseRule(array($this, 'parseRule'), Router::PROCESS_DURING);

This needs a lot of testing.

I agree @SharkyKZ a lot of testing

@SharkyKZ
tested that OK here.
But is'nt the main issue with the modifications of the getInstance() method in CMSApplication between 3.x and 4.0 ?

Closing as we have a patch where this can be discussed further if necessary.
#24332