Try to rename the files.

In what shall i rename the files if Bazooka Sue is searching for

GLÜCK.WAV
LÖWE.WAV
TÜR.WAV
BRÜCKE.WAV
BÜCHER.WAV

etc etc...?

Is there a way to rename the files so that the umlauts are shown correctly and can be found by the games?

I already tried to hex-edit some of the Bazooka Sue code, which causes the game to crash because of an invalid checksum.

Dificult Question. You should try to rename, like the TÜR.wav to TUR.wav. If the game try to search the files, ask the creator of the DOSBOX. And, eh, don't try to hex-edit anything, you can give goodbye to your computer sometimes. 😀

what is the ascii value of that umloated letters ?
which range are they in ?

Ascii Oct are:

Ä 142
Ö 153
Ü 154

(the small letters would be:

ä 132
ö 148
ü 129

- but would not so important in dos)

[in normal dos i could create them with pressing ALT + corresponding numbers]

more infos here: http://www.asciitable.com/

this is the routine that makes file_names for the functions inside dosbox
(e.g. the openfile commands from dos)

1	while (name[r]!=0 && (r<DOS_PATHLENGTH)) {
2		Bit8u c=name[r++];
3		if ((c>='a') && (c<='z')) {upname[w++]=c-32;continue;}
4		if ((c>='A') && (c<='Z')) {upname[w++]=c;continue;}
5		if ((c>='0') && (c<='9')) {upname[w++]=c;continue;}
6		switch (c) {
7		case '/':
8			upname[w++]='\\';
9			break;
10		case ' ':
11			break;
12		case '\\':	case '$':	case '#':	case '@':	case '(':	case ')':
13		case '!':	case '%':	case '{':	case '}':	case '`':	case '~':
14		case '_':	case '-':	case '.':	case '*':	case '?':	case '&':
15		case '\'':	case '+':	case '^':
16			upname[w++]=c;
17			break;
18		default:
19			DOS_SetError(DOSERR_PATH_NOT_FOUND);return false;
20			break;
21		}

You see that the characters you discuss aren't present

well, i'm not a programmer, so i can't make much out of these routines 😉 - so i guess, at the moment, there is no way around that Ü.Ö.Ä - issue? Too bad, becuase all of the games work fine - as long as they don't require that certain files. 🙁

what basicly is written there:
if character doesn't exist in that table
so not a normal character like abcdefghi.... or a number or one of the special characters listed in
that case '\\': case '$' : .....................

then dosbox reports "path_not _found /illegal character in name". and the game can't open the file.

So there is no way around it unless Somebody adds those characters you describe in this table.

To do this: I would need the ascii values and some example games to try it on.