How important for you is to have a different languages available in casinos?
I recently noticed that while many sportsbooks have it (but mostly not implemented very well), most of the casinos or Dice websites don't even bother.
Bests!
Since gambling with cryptocurrencies are getting more popular these days, I guess having a lot of languages on a casino or gambling sites will be a great help since there are a lot of gamblers using cryptos all over the world.
English is the most common language so that will be obvious for them to only use English. Another reason is that they might have a problem hiring some translators for their casinos or sights. Using some translators will not cut it.