This is a proposed improvement for screen reader users (vision impairment) primarily.
The Echo icons' text is not informative: only says "Alert (0)" / "Alert (1)" / "Alerts (2)" / etc. or "Notifications ($1)", etc.
Not an issue for a regular, but for newcomer it's unclear how this element behaves.
I think the following messages would be more helpful due to being more descriptive: PATCH

"tooltip-pt-notifications-alert": "Alerts. Opens popup listing {{GENDER:|your}} alerts.",
"tooltip-pt-notifications-notice": "Notices. Opens popup listing {{GENDER:|your}} notices.",
"echo-notification-alert": "Alerts. $1 unread. Opens popup listing {{GENDER:$1|your}} alerts."`,
"echo-notification-notice": Notices. $1 unread. Opens popup listing {{GENDER:$1|your}} notices."`,

tooltip-pt-notifications-* messages are used server-side (for initial HTML), where the notification count is not available, thus the message does not include a count. The client-side JS updates the message with the count using echo-notification-* message.
This latter message key could be made consistent with the other one (eg. tooltip-pt-notifications-notice-counter.
If needed the count could be included server-side, however I haven't investigated the costs. This would benefit non-JS users (only).

As an added benefit I propose moving the message from the text node - which involves a tricky and problematic solution to hide it, that the web team is struggling with - into the tooltip (title attribute). This solves the hiding issue and also benefit non-screen-reader-users.
PATCH

Steps to test this UX:

1. Run JAWS / NVDA / VoiceOver screen reader
2. Open demo: http://demian-demo.epizy.com/wiki/Desktop_Improvements_volunteer_demo
3. Close sidebar
4. Click in the header
5. Press TAB until one of the Echo icons is focused
6. Listen to the reader
7. Press TAB / SHIFT-TAB to focus the other icon
8. Listen to the reader