MP4 Video Stream Characteristic in Extended tags

Been a while, greetz to all.

So a thing I came across in some MP4 videos I use MP3TAG with is something I discovered using MKVToolnix GUI. Everything MP3TAG does works as expected, but what I can't figure out is how to parse and view the MP4's video stream characteristics. Example, when the file is loaded in MKVToolnix, it show's the videos streams "language" and for the most part it seems that most of the videos language tags are listed as "undefined" i.e. und. In MKVToolnix, I can set them to any of the ISO languages I need allowing correction. Running it through that tool for an MP4 file adds multiple steps since the output engine is MKV, so it would be cool to load an MP4 file into MP3TAG, be able to switch und to eng as needed. MP3TAG seems to do a lot with MP4's now, it seems like that may be just an extra field to be able to change? I've tried a custom column with %LANGUAGE% but nothing shows up. Is there any way to do this? I know MP3TAG has always been mostly for audio but since it has MP4 support, this would be a "nice to have" and I'm asking if it is possible or is there something I can do to make the needed changes.

Thanks,
Chris

Have a look at the list of supported tag fields:


You may notice that the cell for MP4 language is not filled - that would mean to me that MP4 tags don't have a language field.

I did have a look and saw that, it would be great if the support for it one day was there. Clearly it is doable since MKVtoolnix does it, but as mentioned, it is a lot of leg work to have to use it to fix a single tag, it exports as mkv (with stream copies) and then have to use another app to bring it back to MP4. Hopefully support comes around for it. Thanks for the response.