Looks like your username has not been changed on all of the wikis as https://www.mediawiki.org/w/index.php?title=User:Ks-M9 still exists?

No. I've re-created my old name in this log: https://meta.wikimedia.org/wiki/Special:Log/St%C3%AFnger ; I've re-created the name to avoid usurpations and the page showed in MediaWiki is a re-directed userpage of my old name to my current name in Meta.

It is still erroneous to re-create my old name or no? affects in this project? My current name still exists in MediaWiki: https://www.mediawiki.org/wiki/Special:Log/St%C3%AFnger

I tried to rename to "Stïnger" here in Phabricator and it got refused (due to the ï) by the software:

"Usernames must contain only numbers, letters, period, underscore and hyphen, and can not end with a period. They must have no more than 64 characters."

Huh, okay. Despite the ï, perhaps with the "i" should work then here? (only here, in the wikis I've wanted to use the "ï"). At least can be changed in my profile the link to the "MediaWiki User: Ks-M9" to "MediaWiki User: Stïnger"? Thanks.

In T186324#3946450, @Ks-M9 wrote:

Huh, okay. Despite the ï, perhaps with the "i" should work then here? (only here, in the wikis I've wanted to use the "ï").

Yes, that should work.

At least can be changed in my profile the link to the "MediaWiki User: Ks-M9" to "MediaWiki User: Stïnger"? Thanks.

You can only do that yourself via " https://phabricator.wikimedia.org/settings/ > External Accounts" by attaching an LDAP account, and then removing the mediawiki.org Ks-M9 account and then attaching the mediawiki.org Stïnger account.
The other option is to create a new Phabricator account which is linked to your Stïnger mediawiki.org account (and hence keeping an old separate account around).

Okay

I want to keep my history of activities of this account, but using my new name. It is likely complicated to me about the change of settings in the external accounts section. If I need a LDAP account, what is the "shell" account and how can I create/obtain that? (apparently I need a "shell" account to create a Wikitech account). And also, if I have a LDAP account and I'll remove the old MediaWiki user, should appear an option to add the new MediaWiki user?

LDAP account = wikitech account = Gerrit account: https://www.mediawiki.org/wiki/Developer_access
Where exactly says something that you need a "shell" account to create a Wikitech account?

if I have a LDAP account and I'll remove the old MediaWiki user, should appear an option to add the new MediaWiki user?

Yes

https://wikitech.wikimedia.org/wiki/Special:CreateAccount indicates the following when I'm not logged in these wiki: "You're required to choose a shell account name. It must start with a-z, and can only contain lowercase a-z, 0-9, and - characters." the indication it's found under the parameter of the e-mail address. And if I don't have a "shell account", appears an error message: "Your shell account name is invalid. It must start with a-z, and can only contain lowercase a-z, 0-9, and - characters."

At least, can I be renamed here? After we could solve this problem. Stinger is OK to use here. Thanks for your help.

Ah, thanks! As you don't plan to really use shell/terminal/console access I guess so you could enter "stinger" or such.