Without patch
Multilingual site. SEF on. URL rewriting off.
Language filter set to Remove URL Language Code
Setting Users Options as stated
Logged out of backend.
Register new user in frontend through module
User receives mail with link
http://localhost:8888/newfolder/trunkgitnew/index.php/component/users/?task=registration.activate&token=7e11bd55a15e327e6165426c07607d3f&Itemid=103
User clicks to ask for activation
Admin receives emaIl
Link to activate user is
http://localhost:8888/newfolder/trunkgitnew/index.php/component/users/?task=registration.activate&token=aab6a49d027dc7e431181cc9f38df24d&Itemid=103

When clicking I get to login in frontend
Message
The user's account has been activated and the user has been notified about it.

Logging again in backend:
User is activated and enabled.

Therefore I can't reproduce the issue here

So, my question is simple: how do you manage to not have a token?

@infograf768 This is what is in the current release:
https://github.com/joomla/joomla-cms/blob/3.9.23/plugins/system/languagefilter/languagefilter.php#L687
https://github.com/joomla/joomla-cms/blob/3.9.23/plugins/system/languagefilter/languagefilter.php#L699
https://github.com/joomla/joomla-cms/blob/3.9.23/plugins/system/languagefilter/languagefilter.php#L709
And it whipes all the data.

To get into the conditions above you need to have login redirect url set too, together with associations. So I assume I'll have to update the testing instructions.

To get into the conditions above you need to have login redirect url set too, together with associations. So I assume I'll have to update the testing instructions.

Please do as precisely as possible as otherwise it is impossible to check your findings. and the patch.
Login redirect url set to what and where: in the module or in a menu item?
What should be associated?
Do you have some specific menu items?

@artur-stepien
Eager to test, but I still need you update the instructions to reproduce the issue.

1 instance of login module created for each Content Language, each with a login redirect to associated menu items tagged to that language and displaying item(s) also tagged to that language.

In any case, this patch breaks associated redirect urls when the user (even admin) successful login has to be redirected to the user default site language and the current language is not that user default site language.

I discovered a token issue, unrelated to the new user being activated (it is always activated), when the admin has logged out after approval and logins again. Therefore not corresponding to the PR description.

@infograf768 I was testing this from scratch and on a clean installation. And the issue was visible when you set Registration form page Access to Guest (that was done to prevent registered users from seeing registration form) and using Modern router set in Users component options (on Legacy it worked just fine - at least for me). Tried to repeat it multiple times and sometimes it caused errors, sometimes it didn't. Therefore I can't pinpoint the exact set of settings. The only thing I'm sure of is that those 3 lines I provided above will wipe any redirection data after login (when user reaches those conditions). I'll give it a try again in few days outside of Docker machine. Maybe Docker is messing with my results.

@infograf768 I did put the whole process I usedto pinpoint the issue today in Testing Instructions. I'll clear my head and try that again later.

Will wait for any new input from you as your instructions are very confusing.
It would be much more easy to understand if you just first installed the multilingual site when installing a clean Joomla.

Anyway, keep in mind my comment above as your patch is a no-no as is :

In any case, this patch breaks associated redirect urls when the user (even admin) successful login has to be redirected to the user default site language and the current language is not that user default site language.

As we have no News from author for 2 months, closing this.
Can be reopened if necessary