The standardizer is written in Perl. Because of this, it is easiest to install and run it on a computer where Perl is available by default (i.e. Mac OS X or Linux). To run it on Windows, you will need to install something like ActiveState Perl.
Almost everything you need to run the standardizer is contained in this github repository. I recommend strongly that you access the code and data files by installing a git client and cloning the repository to your computer. By doing so, you will be able to keep up with the latest development, bug fixes, and contributions from other users.
If you would rather not mess with git, then you can simply download a ZIP containing all of the files in the repository.
After downloading or cloning, you should run:
$ make install
The one resource not contained in the repository is the Irish n-gram language model (roughly speaking, this is a table of probabilities of seeing a word in Irish if you know the previous two words). These statistics need to be stored a Redis database that the standardizer will access at runtime.
If you have a reasonably large corpus of (more or less) standard Irish, you can build your own n-gram model using the scripts in the model subdirectory. Just place your corpus in a plain text file, UTF-8 encoded, one sentence per line, in the model directory. Then edit the variable at the top of model/makefile to point to the file containing your corpus (do not use the default filename corpus.txt). Then:
$ cd model
$ make
You will need the Redis Perl module, and the Redis server must be running on your machine for this to work. This will take a while to run. When it finishes, you will be ready to start standardizing text.