I just ripped and encoded a file with MC11.1.143 (using Scot Thompson's Flac encoder v 1.5 and decoder v. 1.5) and with Easy CD-DA Extractor 7.5.1 (I don't have a newer of version of this).
Before ripping I replaced the original names with strings that contain all Danish characters that I am aware of. Both files show correct and identical file tags inside MC. Here is a playlist export in XML format that contains all library fields (the first file is ripped with MC):
<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<MPL Version="2.0">
<Item>
<Field Name="Filename">D:\Rip\(Multiple Artists)\1 ÅÆØÁÍÓÚÝåæøáéíóúý ÅÆØÁÍÓÚÝåæøáéíóúý\03 - 3 ÅÆØÁÍÓÚÝåæøáéíóúý ÅÆØÁÍÓÚÝåæøáéíóúý.flac</Field>
<Field Name="Artist">2 ÅÆØÁÍÓÚÝåæøáéíóúý ÅÆØÁÍÓÚÝåæøáéíóúý</Field>
<Field Name="Album">1 ÅÆØÁÍÓÚÝåæøáéíóúý ÅÆØÁÍÓÚÝåæøáéíóúý</Field>
<Field Name="Name">3 ÅÆØÁÍÓÚÝåæøáéíóúý ÅÆØÁÍÓÚÝåæøáéíóúý</Field>
<Field Name="File Type">flac</Field>
<Field Name="Genre">Pop</Field>
<Field Name="Bitrate">912</Field>
<Field Name="Media Type">Audio</Field>
<Field Name="File Size">23442506</Field>
<Field Name="Duration">205</Field>
<Field Name="Track #">3</Field>
<Field Name="Date Created">1142278129</Field>
<Field Name="Date Modified">1142278321</Field>
<Field Name="Date Imported">1142278164</Field>
<Field Name="Date">34700</Field>
<Field Name="Sample Rate">44100</Field>
<Field Name="Channels">2</Field>
<Field Name="Bit Depth">16</Field>
</Item>
<Item>
<Field Name="Filename">E:\Rip\1 ÅÆØÁÍÓÚÝåæøáéíóúý ÅÆØÁÍÓÚÝåæøáéíóúý\03. 2 ÅÆØÁÍÓÚÝåæøáéíóúý ÅÆØÁÍÓÚÝåæøáéíóúý - 3 ÅÆØÁÍÓÚÝåæøáéíóúý ÅÆØÁÍÓÚÝåæøáéíóúý.flac</Field>
<Field Name="Artist">2 ÅÆØÁÍÓÚÝåæøáéíóúý ÅÆØÁÍÓÚÝåæøáéíóúý</Field>
<Field Name="Album">1 ÅÆØÁÍÓÚÝåæøáéíóúý ÅÆØÁÍÓÚÝåæøáéíóúý</Field>
<Field Name="Name">3 ÅÆØÁÍÓÚÝåæøáéíóúý ÅÆØÁÍÓÚÝåæøáéíóúý</Field>
<Field Name="File Type">flac</Field>
<Field Name="Genre">Pop</Field>
<Field Name="Bitrate">917</Field>
<Field Name="Media Type">Audio</Field>
<Field Name="File Size">23579217</Field>
<Field Name="Duration">205</Field>
<Field Name="Track #">3</Field>
<Field Name="Date Created">1142277971</Field>
<Field Name="Date Modified">1142278022</Field>
<Field Name="Date Imported">1142278283</Field>
<Field Name="Date">34700</Field>
<Field Name="Encoder">Easy CD-DA Extractor (http://www.poikosoft.com)</Field>
<Field Name="Sample Rate">44100</Field>
<Field Name="Channels">2</Field>
</Item>
</MPL>
My OS is US English. I have no idea if a Danish OS can make any difference. I have a Finnish OS in one of my PCs and I could give it a try. In general, those accented characters belong in the standard extended characters set and they should work with any Windows system.