I also would be very interested of hearing if someone has found a way to easilytranslate a workflow or has a tool for it. Many times the translation can become an own sub-project (this applies also some other SAP functionality which do not offer proper translation tools).
Basically it is not that hard - you probably just want to translate the "visible parts", and this includes just the dialog tasks: maintain the work item text and description in PFTC (this is a bit annoying since you need to log in with the destination language to maintain the work item text). Many times this is enough. But then if you have user decision in the workflow, these you need to go to translate the step to WF builder SWDD.
If you want to make things perfect, you must maintain all the texts in the workflow itself too (in WF builder in the translation menu): all the step names, outcomes, etc. These texts are visible e.g. in the logs etc. so users will most probably have access to these although they are not in the daily use. Luckily the translation tool in the WF builder is quite good, because it lists nicely all the texts of the workflow, and offers a input field to maintain the translation. And if you are after perfection, you need to go back to translating the tasks - the background tasks which will be visible in the logs...
Then, if the developers haven't translated the possible applications that are called inside the workflow, it really can become a project. For example it can be a huge task to translate a big web dynpro ABAP application (some translations come from data elements, some from OTRs, then you will have the messages, etc.)
Kind regards,
Karri