Recently started getting the following error when trying to run git gui. Googling the issue didn't seem to help much.

Error in startup script: bad pad value "2m": must be positive screen distance
    while executing
"grid $w.bitmap $w.msg -in $ -sticky news -padx 2m -pady 2m"
    (procedure "::tk::MessageBox" line 181)
    invoked from within
"::tk::MessageBox {*}$args"
    (procedure "tk_messageBox" line 2)
    invoked from within
"tk_messageBox -icon error -type ok -title {Git Gui (dev): error} -message {Spell checking is unavailable:

No word lists can be found for the language..."
    ("eval" body line 1)
    invoked from within
"eval $cmd"
    (procedure "error_popup" line 10)
    invoked from within
"error_popup [strcat [mc "Spell checking is unavailable"] ":\n\n$err"]"
    (procedure "_connect" line 28)
    invoked from within
"_connect $this $pipe_fd"
    (procedure "spellcheck::init" line 7)
    invoked from within
"spellcheck::init  $spell_fd  $ui_comm  $ui_comm_ctxm  "
    invoked from within
"if {[winfo exists $ui_comm]} {
	set GITGUI_BCK_exists [load_message GITGUI_BCK utf-8]

	# -- If both our backup and message files exist use the
	#    ..."
    (file "/usr/libexec/git-core/git-gui" line 3954)

At first I thought it's a tcl/tk issue, as related things kept popping up. However then I remembered I was having some dictionary issues not long ago that resulted in an annoying error pop-up from git gui (but it would still let me use the tool after dismissing the popup...).

I did find a fix for that one, but didn't get round to applying it on my home machine before a system update. And then the above happened.

It was only after reading through the whole message I noticed this line:

No word lists can be found for the language...

Oh... Could this really be the same issue?

Yep. And the fix is quite simple:

dnf install aspell-en or the language of your choice