Here's a bit more documentation. First off, the Ren'Py documentation on localization can be accessed here. I don't think there's much you need to know from there before you can start translating. A very interesting guide, which I recommend you take a look at, can be found here.

To create the localization files necessary for your language, you'll have to download Ren'Py (it's free). Boot up the software, take a look at the Tutorial just because it's very informative if you want to dig into the script, and then click on +Create New Project (1). 

If it's the first time you have ever used Ren'Py, it will probably ask you to set up an editor for the rpy files. Go with your preference, I've personally used NotePad++ which you can configure to use with Ren'Py, but any will do.

The name itself doesn't matter as it's not the display name of the project. As you can see, ours is called "Horatio V2", because there was another "Horatio" project before, the very first prototype of Love Thyself! Moving on, pick 1280*720 as display, then just click "continue" on the accent and background colors window because you're about to overwrite them anyway, and it'll create your first working files for the Ren'Py project! Whee!

Then open your files browser, go to your Steam folder, and copy the contents of your Love Thyself folder. By default, the path is something like C:\Steam\steamapps\common\LoveThyself , so just head over to \common, click on LoveThyself, and ctrl+A / ctrl+C that stuff.

Then click on Open Directory> base in Ren'Py, which will open the folder that was created for your project. Ctrl+V in there to copy the contents of the game, and boom, if you click "Launch Project"  it should now basically boot Love Thyself! Just check that it works.

Now, click on "Generate Translations," which will create the required files for the localization of your choice. In "language," type whatever language you're translating into (type the English name for it to keep it easier for everyone, and make sure it's lower case). Then click on "Generate Translations" below it.

Let the thing process, and notice that your game folder now has a new subfolder, "tl", which should contain a subfolder in itself with a bunch of rpy and rpyc files.

Those are the ones you'll be working on. They only include the displayed text strings (and choices, and menus) so as not to mess up with the rest of the script.

They look like this (note that particular look may vary depending on software used. This is, once again, NotePad++ because I'm a simple man):

If you want to get started from that point on, it's easy: just start filling in the "" !

To check the results, you'll have to refer to the guide I mentioned above, which I'll just re-link because I do what I want.

Let us know if you have any questions and we'll help as best we can!