update.php fails with Multibyte string input conversion in PHP is active and must be disabled.

This is a support request. What is the actual runtime value? You can find that on the as shown on this old article: https://www.drupal.org/node/59680 →

I think it’s in the same place for Drupal 9.

@cilefen
Thank you for your response.
I am sorry, but what exactly do you mean by "Runtime Value"?
By the way, I was able to get the php information with phpinfo.

That’s good. What are the runtime values? By “runtime” I mean the effective values in the web platform context, rather than in various configuration files.

This is precisely the code that checks: https://git.drupalcode.org/project/drupal/-/blob/10.1.x/core/lib/Drupal/...

Trimming the title and moved the error msg to the IS.

Thanks for the reply.
I don't know if this answers your question, but I will list below the values of the properties that would be relevant.

Multibyte Support	enabled
HTTP input encoding translation	disabled

Directive	Local Value	Master Value
mbstring.detect_order	auto	auto
mbstring.encoding_translation	Off	Off
mbstring.http_input	pass	pass
mbstring.http_output	pass	pass
mbstring.http_output_conv_mimetypes	^(text/|application/xhtml\+xml)	^(text/|application/xhtml\+xml)
mbstring.internal_encoding	UTF-8	UTF-8
mbstring.language	Japanese	Japanese
mbstring.regex_retry_limit	1000000	1000000
mbstring.regex_stack_limit	100000	100000
mbstring.strict_detection	Off	Off
mbstring.substitute_character	no value	no value

Subscribing because I'm seeing the same error (on the admin/reports/status page) after switching from PHP 7.4 to PHP 8.1.14

On the phpinfo page (accessed from the Drupal status page), the value for mbstring.encoding_translation is Off (local) and Off (master).

Is it safe to operate Drupal (e.g. create or edit nodes) while this error is showing?

Update: my hosting provider uses a system with a ".user.ini" file to store user defined PHP settings.

Originally, this file had the following line (among others):
mbstring.encoding_translation = "off"

If I replace "off" by "0" (zero) in that line, then the warning in Drupal goes away.

I'm not sure which value is "more correct" ("off" or "0"), but perhaps the check in Drupal (link in comment #7) should be updated to test for "off" in addition to "0"? Since the phpinfo page shows "off", I'm guessing it's a valid value.

According to the docs in https://www.php.net/manual/en/configuration.file.php,

; Boolean values can be set to either:
;    true, on, yes
; or false, off, no, none
register_globals = off
track_errors = yes

Are the quotation marks the problem?

OP's php.ini lines did the job for me.
The server was set to "Off" and I was getting the same error until I added the php.ini lines with "0" instead of "Off". No more errors.

mbstring.http_input = pass
mbstring.http_output = pass
mbstring.encoding_translation = 0

I am closing this as there have been no replies. Reopen it if needed.