Weird issue with fonts changing on TextMeshPro elements in editor

So I'm using TextMeshPro and I2 Localization. I've got several languages set up and just about everything is working just fine. I use the same fonts for most of my languages except for (Simplified) Chinese, which uses a separate set of fonts seeing as it's got all the characters. I've got the Secondary Terms set up and it's all good EXCEPT for one thing:

If I change the language in the Unity Editor (for example, by clicking on one of the entries in the Main Term), the font in the TextMeshPro components within the current scene gets changed to the font for this language IF I'm changing between non-Chinese languages (where the fonts are all the same) OR from non-Chinese to Chinese.

BUT if I change from Chinese to non-Chinese, the font is left as the Chinese-specific fonts, and nothing I do from then on except going through and manually changing all the TextMeshPro components fonts back to what they should be will change the font.

If I accidentally change to the Chinese language font at any time in-editor the whole scene is perma-broken if I don't notice the fonts have been stuffed up.

Also, once I'm in this state, the fonts aren't changed even when running in a build - they're stuck using the Chinese font!

Any idea what could be going on or how to fix this would be GREATLY appreciated! We just had to delay an update at the last second because we happened to notice this was busted.

I should say : I think this issue might also happen in-game - If I change to Chinese all is well, but if I then change away from Chinese I get missing characters (especially if I change to Russian), probably because it's leaving all the TextMeshPro components with the Chinese-specific font. I haven't confirmed this for certain though