Unfortunately, some accounts are currently not unique across all our wikis, but instead clash with other users who have the same account name. To make sure that all of these users can use Wikimedia's wikis in the future, we will be renaming a number of these accounts to have "
~" and the name of their wiki added to the end of their accounts' name. This will take place in April 2015. For example, a user called "Example" on the Swedish Wiktionary who will be renamed would become "Example~svwiktionary".
All accounts will still work as before, and will continue to be credited for all their edits made so far. However, users with renamed accounts (whom we will be contacting individually) will have to use the new account name when they log in.
Renaming users locally has been removed to prevent accounts that were global from becoming unattached due to local renaming. Users can request a rename using Special:GlobalRenameRequest on their local wiki or ask for their account to be renamed further here on Meta, if they do not like their new user name.