@Andrew Voronov

Can you please verify one last thing? Is the multilingual environment set up correctly on your site? If you are using the core Joomla! multilingual feature you can test this by publishing the "Multilanguage Status" module in the administration modules.

Lefteris wrote: @Andrew Voronov

Can you please verify one last thing? Is the multilingual environment set up correctly on your site? If you are using the core Joomla! multilingual feature you can test this by publishing the "Multilanguage Status" module in the administration modules.

Hi. You may look at my web site and see that it is multi lingual. At right you may see a lang switcher. Switcher works well.
Here is an image of my multi lang status on admin page (from web version of the web site).

@Andrew Voronov

I cannot verify the issue. Just tested K2 2.6.9 under Joomla! 3.4.4 and it worked fine for me. I suggest to try the following:

1. Update Joomla! and K2 to their latest stable version.
2. Check for any third-party system plugins. Try to disable them one by one.
3. Try to disable URL rewriting by setting " Use URL Rewriting" to "No".
4. Check your .htaccess file. Copy Joomla's htaccess.txt contents inside your .htaccess file.

@Lefteris

I don't know what to say.
I have local copy of the web site and tried all 4 steps that you wrote and it didn't solve the issue.
I don't know how to prove it.. may be using screen sharing?!

Andrew, I 'm sorry but I cannot confirm the issue.
Which other extensions are you using?
Can you send me your htaccess file?

Yes, I can... but attachment form doesn't work. I can even send you a link with a project on github github.com/pupsikus/iman007
I don't use 3rd part extensions for storing content or for SEF. A turned off all extensions (except K2 and core extensions) and it didn't help.

It is possible that problem is in the template (Meet Gavern), but I am not sure about it.

@Andrew Voronov

I don't think that the issue is caused by your template. Have you checked the .htaccess file as i suggested? Have you tried to disable URL rewriting by setting " Use URL Rewriting" to "No" in Joomla! global configuration?

Yes, I tried to switch off URL rewriting, after switch off, my url looks like this: /index.php/en/tag/Android.html , but it still shows 404 error.
Here is my .htaccess file content (without unnecessary commented text). I don't see here any issues

## No directory listings
IndexIgnore *

## Can be commented out if causes errors, see notes above.
Options +FollowSymlinks
Options -Indexes

## Mod_rewrite in use.

RewriteEngine On

# Block out any script trying to base64_encode data within the URL.
RewriteCond %{QUERY_STRING} base64_encode[^(]*\([^)]*\) [OR]
# Block out any script that includes a <script> tag in URL.
RewriteCond %{QUERY_STRING} (<|%3C)([^s]*s)+cript.*(>|%3E) [NC,OR]
# Block out any script trying to set a PHP GLOBALS variable via URL.
RewriteCond %{QUERY_STRING} GLOBALS(=|\[|\%[0-9A-Z]{0,2}) [OR]
# Block out any script trying to modify a _REQUEST variable via URL.
RewriteCond %{QUERY_STRING} _REQUEST(=|\[|\%[0-9A-Z]{0,2})
# Return 403 Forbidden header and show the content of the root homepage
RewriteRule .* index.php [F]
#
## End - Rewrite rules to block out some common exploits.

# Uncomment following line if your webserver's URL
# is not directly related to physical file paths.
# Update Your Joomla! Directory (just / for root).
##

# RewriteBase /

## Begin - Joomla! core SEF Section.
#
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
#
# If the requested path and file is not /index.php and the request
# has not already been internally rewritten to the index.php script
RewriteCond %{REQUEST_URI} !^/index\.php
# and the requested path and file doesn't directly match a physical file
RewriteCond %{REQUEST_FILENAME} !-f
# and the requested path and file doesn't directly match a physical folder
RewriteCond %{REQUEST_FILENAME} !-d
# internally rewrite the request to the index.php script
RewriteRule .* index.php [L]
#
## End - Joomla! core SEF Section.

Also, I don't understand such thing.... I have category "blog" and subcategory "it". When I go to category list using menu item my url is: "/en/blog.html" (blog without id) When I go to item my url looks like this: "/en/it/7-it/21-how-to-choose-smartphone-correctly.html". Why url doesn't show top category "blog" and why subcategory "it" shows 2 times: with and without id ? I have the same "blog/it" categories url in "ru" language and it is OK to show id in category items and materials. Everything works properly even I have the same urls... all except tags. Maybe url"/en/tag/Android.html" also should go with id (tag-id)?

Can you try to switch off K2 advanced SEF? At least we can see that the issue is coming from there. Remember to clean Joomla! cache after you make the change.