This is an important topic of development for Open Steno. Machine shorthand has existed in many languages and is used in many countries.
However, not all of them are "computer" or "realtime" compatible, which roughly means that you wouldn't be able to distinguish in your writing between homophones like "their" and "there" and "they're."
Overall, I'd say that coding speed doesn't really change as typing fast is not what makes coding fast.
There are some real advantages that I find difficult to quantify, though. I switch between stenography and typing for both coding and writing depending on whether I'm at my desk and I find it hard to express clearly why coding in stenography feels natural and nice. I suppose: there's a certain fluidity when you break things down into semantic words rather than simply symbols.
I'm the author of Art of Chording—I program full-time with steno in JavaScript (working mainly with React.)
I'd love ideas on how to demonstrate coding in steno. I struggle with it sometimes because the slowest part about coding is not the input rate… it's the brain. I guess if people are looking to code "quicker"… it's not the rate of input that one would want to explore. I will say that writing comments became a lot easier when the words started to just flow onto the screen.
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Unhelpful catch-all responses that don't display a shred of effort or care are the bane of my customer support experiences. Nothing hurts my opinion of a company like being brushed off like a bug.
However, not all of them are "computer" or "realtime" compatible, which roughly means that you wouldn't be able to distinguish in your writing between homophones like "their" and "there" and "they're."
Here's a list of some of the languages that have been developed or ported to Plover: https://github.com/openstenoproject/plover/wiki/Chorded-Syst...
There is a Plover plugin to switch on-the-fly between different steno systems.
There is also a plugin to switch between enabled dictionaries on-the-fly.
Finally, there is the idea of bilingual dictionaries, but I haven't seen it implemented well yet.
There's also the problem of some languages having drastically different layouts.
So far, the most multilingual and successful stenographer I've seen is Stanley Sakai. Here's him writing in a Spanish theory that he developed: https://www.youtube.com/watch?v=eGZ43TID9jU&t=90s
I also know that there are bilingual stenographers in Canada who write both English and French, but I haven't seen it in action yet.
In summary, I think that multilingual stenography is critical for the adoption of steno, but it's currently not easily accessible or widely used.