Symptoms

Any Word or Excel export which is done when using a filter which a search text of an string with umlauts will return zero results.

Cause

The cause of the problem was that the parameter useBodyEncodingForURI="true" is not set. This causes umlaut characters to be lost when the export is made. Example:

<Connector port="8080"
      maxHttpHeaderSize="8192" maxThreads="150" minSpareThreads="25" maxSpareThreads="75" useBodyEncodingForURI="true"
      enableLookups="false" redirectPort="8443" acceptCount="100" connectionTimeout="20000" disableUploadTimeout="true" 
/>

Resolution

Add useBodyEncodingForURI="true" to server.xml and restart JIRA.