The bug
Whenever you enter a portal (nether or end), normally a message that says Entering the nether and/or Leaving the end would appear. It's been happening ever since singleplayer became multiplayer-managed in 1.3.
How to reproduce
Create a nether portal or repair an end portal
Enter the portal
Related issues
is duplicated by
relates to
Comments

How is this a duplicate of MC-233? That issue is about sound, not messages, and @unknown has said in the comments of that issue that this is a separate issue.
Agree. This is not a duplicate.
Affects 16w04a.
Affects 16w05b.

Probably relates to MC-2681
Affects 16w06a.
A related bug was marked as works as intended, so I guess this is intended too.
Affects 16w07a.
Affects 16w07b.

"Simulating the world for a bit" (menu.simulating
) does not appear anymore neither even though it is still listed on crowdin
Affects 1.9-pre1.
Affects 1.9-pre3.
Affects 1.9.1-pre3.
Affects 1.9.2.
Affects 16w20a.
Affects 1.13-pre1

@unknown, ticket is yours now.
Confirmed for 1.13.1.
Confirmed for 20w11a
Still in 20w12a
Affects 20w13b
Affects 20w18a
Affects 20w19a
Affects 20w21a
Affects 20w22a
Affects 1.16 Release Candidate 1
Affects 20w27a

Affects 20w28a

Affects 20w29a
Affects 1.16.2
Affects 1.16.3-rc1
1.16.3 has been released?
Can confirm in 20w51a.
Can confirm in 21w03a.
Can confirm in 21w05b.
Can confirm in 21w06a.
Can confirm in 21w07a.
Can confirm in 21w11a.
Can confirm in 1.16.5 and 21w14a.
Can confirm in 21w15a.
Can confirm in 21w17a.
Can confirm in 1.17.

Can confirm in 1.17.1 Release Candidate 1.

Can confirm in 21w39a.

Can confirm in 21w40a.

Can confirm in 21w41a.
Can confirm in 1.18.1.
Can confirm in 1.18.2.
In 22w15a
Can confirm in 1.19.
Can confirm in 1.19.2.

Affects 1.20.1.

Would this count as a parity issue?
Predates busy bees, so no.
In 23w32a
In 23w33a
In 23w35a
In 1.20.2 Pre-Release 2
In 1.20.2 Pre-Release 3
In 1.20.2 Release Candidate 2
In 1.20.2
In 23w42a
Duplicate of MC-2097. Please use the search function to check before posting in the future.