Runtime Packages were intended to be a common asset library of graphics, music, and sounds that games often shared to save on disk space in the early days of computing (where floppy disks and dial-up modems were commonplace). A good way to understand the way it's used is through Microsoft's tools; developers that use Visual Studio often include Visual C++ Redistributables and the .NET Framework, or they have to tell the user to download it from Microsoft's website.
The installer for the RTP is given out by RPG Maker's vendor at their homepage for anyone to download but not to share.
The better games often don't use this package to ease the burden of having to install more prerequisites just to get the game working, and because they use original assets that the RTP would have no use replacing. You can use official packages from RPG Maker 2000 and 2003, but they can't be shared around, and they can't be used for projects that weren't made with anything other than RPG Maker (like EasyRPG, unfortunately).
EasyRPG is free and open-source, so our own RTP replacement (which is incomplete) would need to follow the same share-alike rules of our license.
The websites linked below are written in Japanese. Scroll down to the bottom of these files and click over the long blue button to download the RTP files.
Depending on the operating system you have to take care on a few steps:
IMPORTANT: The official installers encode Japanese text in JIS, not Unicode. You'll need to set your computer's language and/or locale to Japanese before the installation can work properly.
You can do this easily using LocaleEmulator: http://i.watashi.me/archives/locale-emulator.html with Windows 7 or later. For legacy Windows (XP/2003) you can use AppLocale: http://www.microsoft.com/en-us/download/details.aspx?id=13209 and still install AppLocale on Windows 7 by running the msi installer with legacy operating system emulation, or by following this guide.
Just install the RTP using the official installer, the Player will automatically find it by reading the registry.
WINE has a registry, and EasyRPG Player can read RTP paths from it much like RPG_RT does for Windows.
Install the RTPs in WINE, and then the Player will automatically find and extract it. You can then optionally uninstall WINE if the RTP was all you installed in it; under WINE, this procedure only ensures a valid install.
Because RTP are Japanese shift JIS encoded and they are not Unicode, you will need to execute them with a different locale if your UNIX default locale is not Japanese. You need to have the ja_JP.UTF-8 locale generated. Check your distribution locale configuration if you need to enable it (can vary between distributions). Once RTPs are installed you can disable this locale again.
By following the instructions below you will be able to install them:
From a terminal window, go to the working folder where RPG2000RTP.exe and RPG2003RTP.exe files have been unpacked, then run:
LANG=ja_JP.UTF-8 wine RPG2000RTP.exe
LANG=ja_JP.UTF-8 wine RPG2003RTP.exe
For systems that can't (or don't want to) use WINE for its registry auto-detection, you'll need to copy RTP files from a preinstalled RTP manually.
EasyRPG Player reads these environment variables for the packages:
RPG2K_RTP_PATH: For the RPG2000 RTP
RPG2K3_RTP_PATH: For the RPG2003 RTP
RPG_RTP_PATH: For any RTP (a fallback if one of the others hasn't been filled in)
If your system does not support environment variables, just place the RTP in the folders
Extract the RTP into
/data/rtp/2003 (SD and USB are supported).