It's been done before (Germany during the Third Reich, Russia during the Cold War), but even though the scientists involved did some really good work, they couldn't do as much as they could have in cooperation with the rest of the world (a lot of work done abroad was duplicated).

There's a reason science has always been so international - it just makes the research process a lot quicker and more effective. And a common language helps enormously. In the Middle Ages (and for quite some time after) the lingua franca of science was Latin. That changed around the 18th-19th century, when a lot of work started being done in local languages (Mendel wrote his findings up in German, Darwin in English, Pasteur presumably in French, etc.) This meant that to stay on top of your field as a scientist you had to understand all the important languages (English, French, German, some Italian and Russian). After WWII, English became the new Latin so to speak, and we had a predominant language again.

So to sum up, if you are prepared to risk scientific isolation, go ahead and do your own thing in your own language - if a nation state is set on doing something like this, it will manage at an academic level. But in today's globalised world, I doubt whether any commercial/industrial players would be able or even willing to pull it off.