Class 'JString not found Joomla 4.0

[Kikiyo]

Similar here, using Macedonian language pack.
Replacing "JString" with "StringHelper" in "public static function transliterate", and adding "use Joomla\String\StringHelper;" just below "defined('_JEXEC') or die;" solved the problem partially.

Now there is "An error has occurred.
0 Call to a member function get() on null" on the main Administrator menu link "Home dashboard" showing.

[gamod]

I also got this error in the Hungarian language pack, but I fixed it. The Joomla 3 Hungarian language pack includes an hu-HU.localise.php, which has a transliterate function that uses JString, but Joomla 4 no longer includes JString.
In the transliterate function I replaced the following line:
$str = JString::strtolower($string);
for this line:
$str = StringHelper::strtolower($string);
Also, after the header, I added the following line:
use Joomla\String\StringHelper;

localise.php.txt

Thank You!
Your modified php file saved my Hungarian site!

[Krisi]

I got the same problem after upgrading to Joomla 4.2.5 on a multi-language website.
I did all the pre-upgrade preparations.
Purged Akeeba and FOF files.
Everything works well except this error on at least the main page in Czech language.

[Krisi]

Also, after the header, I added the following line:
use Joomla\String\StringHelper;

where exactly to put that in?

[jankorshavn]

I have a Bulgarian language package and had the same Error.
After changing $str = JString::strtolower($string);
to
$str = StringHelper::strtolower($string);
and the header addition, everything works perfectly.

It looks like I have the same problem with my norwegian site, but adding these suggestion in the nb-NO.localise.php didn't do the trick. In advance I have uninstalled most extensions listed in the pre-update check.. Any suggestions?

[proximos]

easy way to fix this problem. after update, erase /language and /administrator/language and install again

[israelguido]

I disable this two plugin:
- Content - Script Code Highlighter (GeSHi)
- Button - Script Code Highlighter (GeSHi)
And reinstall the site language, in my case is PT-br

[andraspal]

I fixed this just by changing the default language in phpmyadmin com_languages table to en-GB and deleting the other language from _languages table (the latter may not even be neccessary). Then just reinstalled the deleted language.

[pishro]

I reinstalled it and it was fixed
Thanks friends

[cranbaries]

I also got this error in the Hungarian language pack, but I fixed it. The Joomla 3 Hungarian language pack includes an hu-HU.localise.php, which has a transliterate function that uses JString, but Joomla 4 no longer includes JString.
In the transliterate function I replaced the following line:
$str = JString::strtolower($string);
for this line:
$str = StringHelper::strtolower($string);
Also, after the header, I added the following line:
use Joomla\String\StringHelper;

localise.php.txt

Thanks

[Johan Jonker]

What worked for me is disabling the dutch language by renaming the map nl-NL to nl-NL-X.
Then reinstall the dutch language.