Hi Milena,
I've never used Tortoise Git, but looking at
this blog post it shouldn't be too hard. Most likely, you skipped the first step of installing either msysgit or cygwin. I've done both in the past, but most recently I've used the first link from
this msysgit page, which worked well. Be sure to restart your computer as it mentions.
Once you've got git going, the real work can begin. For each of the OMERO clients, there's going to be significant effort needed to refactor all the English elements out of the UI and into configuration files, which you can then translate into Spanish. The style of configuration will be different for Java and Python. Which client is more important to you? .insight or .web?
If you start commiting changes to your git repository, then we should be able to help you review your changes and most effectively get them back into the mainline. Or, if there's anything else we can do to help you get started, just let us know.
Cheers,
~Josh