For words "Day", "Biome", "Score" and other.

Doesn't really make sense adding them to the mod itself as those could be a standalone resource pack.

And how to create standalone resource pack? And how it should work?

Basically it's the same as a (texture) resource pack. Except the only thing it contains are the language files. You put it into the same folder as the texture packs. I could make a repository for that, but I don't really have the time to maintain the things. At least now at the moment, still trying to finalize 1.6.4 builds of my mods.

Here's the thing. If you and any other translators (@Vexatos maybe?) can compile a list of things that could be useful I'm willing to make a repository for it. I don't need the message.key.whatever stuff, just a list of words that are common enough to be useful. Having a little script for my other repositories, so I can as well put it to a good use. I can name it InGameInfoXML ExtraLocalization or something along the lines (or a more general name, as this won't be exclusively for IGI).

You need translation?
Day - День
Biome - Биом
Light - Свет
EXP - Опыт
FPS - FPS(like in English)
Entities - Существа
Now you have Russian translation.

No, @Lunatrius meant you/we shall list all the entries that could be translated, so he can add those.

Still nothing?

I've been mostly working on code, put this one off to the side. While it seems like a great idea, I kind of don't see the use case for it. I'm not sure that anyone would use it and in IGI it would cause a bit of a slowdown if it's overused.

Created IGI-Resource-Pack, will push the basic stuff soon.