How to use german "Umlauts" to label plot axis

[Alaak]

Hi,

I tried to plot some figures which need to have German umlauts (i.e. 
äöü) and the ß character. But I only get gibberish and the error message

warning: ft_render: skipping missing glyph for character '�'

This seems to mean I am a victim of bug: http://savannah.gnu.org/bugs/?31596

Is there a solution or workaround for this problem?

Thanks and regards