The last post I can see in you profile that says French was to [email protected]
That community doesn't accept posts in 'unspecified'. In their API response, it says: "discussion_languages": [47]
47=French. If it also allowed unspecified, it would say [0, 47]
So it may be that you're selecting 'unspecified', but in order for it to actually post, it's going through as 'French'. This is probably better than just erroring.