This requires case-insensitive completion of two+ words where the the prefix in a word contains the single-byte lowercase form of the multi- byte character occuring in the same position in an earlier word.
The words here start consist of one of the following followed by `-': U+212A KELVIN SIGN U+006B LATIN SMALL LETTER K Reproducer: echo 'set completion-ignore-case on' > irc INPUTRC=irc bash --norc -i <<< $'complete -W "\u212A- k-" f\nf \t' ================================================================= ==2838==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x00397f5ee2b3 READ of size 1 at 0x00397f5ee2b3 thread T0 #0 0x587fdb10e8 in compute_lcd_of_matches lib/readline/complete.c:1388:54 #1 0x587fdb0428 in rl_completion_matches lib/readline/complete.c:2330:5 #2 0x587fbbc7f8 in attempt_shell_completion bashline.c:1769:14 #3 0x587fdab1b4 in gen_completion_matches lib/readline/complete.c:1260:17 0x00397f5ee2b3 is located 0 bytes after 3-byte region [0x00397f5ee2b0,0x00397f5ee2b3) allocated by thread T0 here: #0 0x6fe1752874 in malloc (/data/data/com.termux/files/usr/lib/clang/18/lib/linux/libclang_rt.asan-aarch64-android.so+0xed874) #1 0x587fc1b2c4 in xmalloc xmalloc.c:104:10 #2 0x587fd34944 in strlist_copy lib/sh/stringlist.c:126:17 #3 0x587fd366a0 in strlist_append lib/sh/stringlist.c:164:18 #4 0x587fc080a0 in gen_compspec_completions pcomplete.c:1311:10 #5 0x587fc118d8 in gen_progcomp_completions pcomplete.c:1528:9 #6 0x587fc108fc in programmable_completions pcomplete.c:1581:13 #7 0x587fbbbccc in attempt_shell_completion bashline.c:1718:28 #8 0x587fdab1b4 in gen_completion_matches lib/readline/complete.c:1260:17