Where are the items 298 and 302 applied in the game? My team and I are translating this project into Chinese, but we haven't found such descriptions in the game. Where are these projects applied? Is it used to display versions?

I would recommend settings up either the full mod project in an IDE such as IntelliJ IDEA, or at least adding the mod sources in a project in a text editor so that you can search for any occurences of the string in the entire project. At least in Sublime Text you can do that to find where (if anywhere) the localization strings are used. Although that will only get you the code location, it might still not be clear from that where it actually would appear in-game.

Also note that there will be major changes, refactoring, clean-up and re-organization of the localization strings very soon, starting in the 1.12.2 LiteLoader branch (which is not yet on GitHub, but it's the continuation of the current public master branch). So you might want to wait on localizing Litematica. The other mods (malilib, Item Scroller, MiniHUD and Tweakeroo) have had some of these changes done already, at least they now have the config names and comments in the lang files, although I'll still need to go through all the config tooltips and update and improve them in some places. And I also want to slightly clean up and re-organize some of the localization key naming conventions.

And to answer the original question, it looks like the currently_open_project line is not used anywhere atm:

The version_entry is used in the project/VCS version entry widget text:

Oh, OK, then I'll tell them that you've worked hard. It's a pity that I'm just an ordinary Chinese player and don't have a bank card that can use US dollars to remit money for you. It's a pity.