Hi @lasselauch,
thank you for reaching out to us and I am sorry to hear about your problems regarding targeting multiple localizations. I am struggling however a bit to understand what is exactly going wrong for you. You tell us that the plugin "isn't behaving correctly in R23" which is a bit too broad for us to come up with an reliable answer. I am also sorry for having to point out that your proposed way of getting hold of the implementation of the plugin via aescripts.com - with the proprietary downloader you provide there to distribute your products - is a bit much for us.
I would suggest that you share the relevant code more directly here, or, in case you cannot do this, share it via sdk_support(at)maxon.net confidentially with us (please note the Forum Guidelines regarding Support Procedures: Confidential Data, specifically regarding NDAs, in case they would apply here).
For your actual problem: It is really hard to give any advice without knowing what exactly is going wrong. I assume you have a Japanese localization in your resource folder and it does not work for the user? I would check:
If the folder has the correct ISO 639-1 language code, for Japanese it should be ja-JP, so for the strings folder it should be strings_ja-JP for example. Not providing a matching language code for a running Cinema 4D instance should result in Cinema automatically falling back to en-US.
Make sure that the Japanese translation files are all UTF-8. While the manuals do not state that restriction, it could be something that is tripping Cinema up, especially considering that languages with large character sets, like for example Japanese, are not fully represented in UTF-8 due to the limited namespace. I would however had to ask our translators how they handle Japanese if this is the culprit.
But in the end these are mostly shots into the dark for me, due to not knowing what is exactly going wrong. So I would also had to ask you to describe more precisely what is going wrong.
Cheers,
Ferdinand
