non-US characters are not supported in filenames.

DOSBox use default CP 437 for the file system.
And currently there is no way to change the CP in DOSBox. (No DISPLAY.SYS loading, nlsfunc or chcp).

I noticed it also doesn't work when in booted dos. I mean i cannot even type non us characters, although display.sys, mode, keyboard.sys was loaded fine from config/autoexec. Am I doing something wrong or it should be like that? Also as i don't remember does it mean it won't work in booted windows9x too (don't remember now and right now i only have us installed)?

Am I doing something wrong or it should be like that?

The first, this is fully a software-only problem then (char translation to/from the disk image which is done by dos/dos device drivers).

you can check it yourself

it works on real computer but doesn't in dosbox
all the characters I typed at the end should be polish letters, but are not
and z should be swapped with y, but is not

c:\>ver
MS-DOS Version 6.20

Err, Robertmo, you forgot the country= command in the config.sys.
Read this.

country is for regional settings (check how it looks in windows)

Yeah dunno, looks fine and should work that way.

it looks codepage 852 is working as files are displayed with foreign letters and also i can type them with alt 224 for example.
Also it looks all keyboard layouts using that codepage (852) doesn't work in dosbox with booted dos.

Dosbox emulates MS-DOS. MS-DOS 6.x and below only allows ASCII filenames (so no åäö).

MS-DOS 6.x functionality:
* Treat file names stored on the disc as a string and print the string out on the screen without any character set conversions.
* Generate an error message if you try to create a file or directory with a name containing non-ASCII characters.
* Generate an error message if you try to access a file or directory with a name containing non-ASCII characters. A different OS (e.g. PC-DOS) is needed to create the file in the first place.

Dosbox appears to emulate the MS-DOS 6.x behaviour perfectly (see image below), so I assume that there is no bug.

theres might be problem in how dosbox communicates the non-ascii file names to host OS too, IF this were done by mounting directories and not disk-images.

i've made a batch file to creates 128 files each using a character > ALT+0127

Dosbox 0.74 (plain), under winXp English (CP 1252), only 5 files were created on mounted directory.

using winxp NTVDM, only 117 were created.

using real dos this should creates all 128 files, but i doubt Windows could actually read them.

using real dos 6.20 on real computer it creates 109 files (same as using dos 6.20 booted in dosbox) using default English codepage. For example using polish codepage in dos on real computer it creates only 88 files.

DOSBox rejects the creation of files that have names that look like random memory. This is to prevent DOSBox from flooding the harddrive with odd files incase the emulation goes haywire. It is one of the oldest sanity checks in the DOSBox emulated DOS.

Again foreign characters in filenames are NOT supported and will not be.