Using dead keys acute and grave/backtick in normal mode doesn't work

Steps to reproduce

I'm using macOS with a German locale and a German keyboard where ´ (acute) is a dead key and ` (grave/backtick) is produced by hitting shift and ´.

It easier to type ´ as it does not require the shift key. Thus in my .vimrc, I have defined: nmap ´ `

This works fine in Terminal of macOS!

In MacVim, neither ´ nor ` works.

For vowels, I got it working with mappings à la:

nmap ´á `a
nmap ´Á `A
nmap `à `a
nmap `À `A

But this does not work for consonants like b. The error is raised: E78: Unknown mark

Expected behaviour

Both ´b and `b should jump to the mark.

Version of Vim and architecture

9.1.727

Environment

OS: Sequoia, arm64
Terminal: macOS Terminal
$TERM: xterm-256color
$SHELL: /bin/zsh

How MacVim was installed

Homebrew

Logs and stack traces

No response

Vim configuration where issue is reproducable

No response

Issue has been tested with given configuration

• by running MacVim.app from GUI macOS interface
• by running vim/gvim/etc installed by MacVim
• by running other versions of vim (e.g. /usr/bin/vim)

Issue has been tested with no configuration

• by running mvim --clean (or gvim, supplied by MacVim distribution)
• by running vim --clean (in terminal, supplied by MacVim distribution)
• by running vim --clean (in terminal, other suppliers, e.g. /usr/bin/vim)

Other conditions

• The both Homebrew packages "vim" and "macvim" are installed

Start by reproducing the issue in MacVim.app with mvim --clean, then compare it with vim --clean in macOS Terminal using the documented acute and grave mappings. Trace MacVim's handling of dead-key input and normal-mode mark motions; done means both ´b and `b jump to the corresponding mark without E78.