Run the JRE installer in Spanish and Swedish using the command "jre.exe /lang=${langID}", with langID equal to 1034 and 1053. Anytime you re-install the JRE, the localized text that gets used with the installer is the one that was previously used during the last installation. Follow these steps:

- Install in Spanish: "jre.exe /lang=1034"
- re-install in Swedish: "jre.exe /lang=1053"

Notice during the re-installation, everything is still in Spanish and not Swedish. You have to re-install in Swedish once more to see all of the windows in Swedish.
I tested this using JRE 6u10-b10 on WindowsXP.