I use Oxygen which has a nominal fee. I like this option because it comes with a development environment which allows me to step through the execution and set break points to jump to a particular line in the input or a particular template in the style sheet.
A free command line options is Saxon. (See: https://saxon.sourceforge.net https://saxonica.com))
Microsoft provides a command line tool. Remember to use the -xe switch.
Microsoft C# (and other languages) include XSLT processing. The express version of these languages can be downloaded for free.
Python also will process XSLT. A script can embed the transformation if desired. It relies on installing lxml (which is a Python add on module for processing XML files.)
You can learn using the online tutorial.
Webonary gives language groups the ability to publish bilingual or multilingual dictionaries on the web with a minimum of technical help.
With lexical data in FLEx, the process is simple: 1. 
