Under Engraving Options/Language there’s a setting called Tempo Objects Language. If I change this to French, I would expect all the Italian defaults like Lento and Tempo primo to change into Lent and 1er Mouvement, but all the choices remain Italian. Am I missing something?
This was originally something that we intended to do, but then on further investigation turned out to be Not Quite That Simple, as many of the existing terms may not translate exactly to every supported language, and then you have the further combinations of meno/molto/mosso/piu, etc which needs to be done in a grammatically correct manner in each language. It’s likely to be something that we’ll look at again in a future version.
Good to know. I was also wondering how something that complicated could be integrated, especially in v. 1.0 and I can very well understand that it turned out not to be as simple as it might have seemed from the outset.
There are many areas of Dorico that turned out to be not as simple as might have seemed from the outset!
“Before I had studied Zen for thirty years, I saw mountains as mountains, and waters as waters. When I arrived at a more intimate knowledge, I came to the point where I saw that mountains are not mountains, and waters are not waters. But now that I have got its very substance I am at rest. For it’s just that I see mountains once again as mountains, and waters once again as waters.”
Keep going - it will get simpler eventually 
So, 3 years later and no change? At the very least the Option should at least be removed so as not to give false hope.
To be honest, I don’t think I’ve ever used anything at all in the right hand Tempo panel in the past three years, except the tempo equation option once or twice.
Who cares what the default language is - just type the words, and the MM mark, that you want to use.
IMO many of the built-in MM marks are at best “strange”, and ordering the list in terms of somebody else’s idea of relative tempos makes finding anything a “scroll up and down until you see it” experience - which takes a lot longer than just typing something. There is a huge amount of music where Allegro means something more like MM 104-108 than 140, to just give one example.
The division between “relative change” and “gradual change” is a bit arbitrary as well, since most composers probably used a different music dictionary from the development team (assuming they used one at all).