Maybe it would be good to have that as an option.
Personally I like having three separate streaks, easier to keep track of progress in each language separately and stay motivated each day, etc. But others might do separate languages on separate days of the week, or jump from language to language as interest dictates, and would still want to see something for their hard work.
In the current design, each language has its streak, meaning there are already multiple streaks.
In the iOS widget, you can only display one of the streaks.
My suggestion is to add a new aggregated streak on top of current per-language streaks. I can then choose to display this aggregated streak in the widget.