Hi! Yes its possible :D
I'm very new to ren'py so I'm not sure about the issues you've been facing with the files :(
We can deal with them.
1. There is an SDK tool to generate the translation files. You can see the picture below.
2. This is only the text file. You should add a new font to support CJK characters.
3. Since you have some images with text, they should be edited by Photoshop, and be overwritten with the originals.
As I said before, they are image assets. You can find them under the image folder(e.g. game\images\buttons). And they can be translated by replacing them. You can edit them in Photoshop or some other photo-editing software.
Another thing is that, plz inform the devs that your specific language. It is not Chinese, but Simplified Chinese or Traditional Chinese. As a player, it should be fine; but as a translator, it should be strict.
Have fun translating!