@bartlomiej.styczynsk - Would the JavaScript API suffice? The getCurrentUser method will provide the current user object containing the user’s Atlassian AccountID.
@david2 - Thanks for that. I’ll raise the issue of the omission of the opt in mechanism with both teams to try to sort it out.
Hi @jens,
Thanks for your comments regarding performance concerns, however the request should not necessitate a call to the Jira/Confluence server as the timezone state will be available in the host frame. This means that your rendering will be asynchronous, but with minimal delay. This is also in line with our encouragement of apps to use the cacheable app iframes pattern.
Personal data is still returned (such as is visible to the person doing the lookup), just not username.
For JQL, a query like assignee=daniel can do a partial match against any personal data as is exposed by that person. That is, if the person lets you see their display name or email address, then this query may match that person’s display name or email address. This will continue to work.
Hi @jens,
In addition to my previous response, would it help if we could provide a method AP.user.getLocale()?
Hi @akassab,
Unfortunately, the JavaScript API will not be sufficient. When running frontend we’re already in the context of some Jira Cloud instance and it’s already too late (many technicalities require us to have our addon’s accountId in runtime prior to or during interacting with the first Jira Cloud instance). Is that possible?
Hi @dmorrow
thanks for clarifying this!
We are not yet using cacheable iframes because we require condition expressions such as isSpaceAdmin={condition.space_function_permission(permission=SETSPACEPERMISSIONS)} in iframe context parameters and those are not supported in cacheable iframes context (but that’s a different topic).
Yes, that would help a lot for the UI iframes, but not for static connect macros. However the latter limitation is not an issue for us at this time, so I’d be glad to use a potential AP.user.getLocale() along with AP.user.getTimezone() 
Is there already a Jira issue to watch for this?
@bartlomiej.styczynsk - I’m not familiar with any other methods then. I am checking with a few people to confirm if there’s not an alternative available.
@bartlomiej.styczynsk, I’m afraid that isn’t possible at the moment. I have raised [AC-2484] - Ecosystem Jira to track your request.
Closing this topic. Please see Weekly GDPR API status development update - February 28th - #5 by jmort for the latest.