Obj file with german umlauts problem

I have a obj file with german umlauts in the filename. WHen i import it it already looses the texture. When i export it then it writes the filename with umlauts, but in the *.obj part the umlauts gets destroyed.

The mtl file is called umlautstest_nvil_äöü.mtl, in the *.obj file you can read mtllib umlautstest_nvil_äöü.mtl. And then it`s clear that the obj part doesn`t find the mtl part anymore.

I know that the Obj file format specification doesn`t allow umlauts. But all other apps i know work around this by simply allowing umlauts. The standard gets overwritten by a quasi standard here.

Could you please work around the standard too, and allow umlauts in a obj file?

Attached my test case. A simple cube with a checker texture.

I can get the reading work. But not sure about the writing, it does not work on my pc.

That would be at least something