File.fnmatch doesn't match german vowels

I have an issue when Rails is resolving the view templates and the template paths contain the german vowels ä, ö or ü.
When using Ruby 2.2.2 the following will match and return true:

``` ruby
File.fnmatch("#{Dir.pwd}/exämple.txt", "#{Dir.pwd}/exämple.txt")
```

But when using JRuby 9K this will actually return false. 
