luatex problem with file with umlauts on windows 10

[Akira Kakuto]

Dear Ulrike,

> How does the functions know how to convert? I mean how is the "local
> code page" defined or queried?

local code page is obtained by win apis,
int syscp = AreFileApisANSI() ? GetACP() : GetOEMCP();

Best,
Akira