Other than China and India, no other market is as big or insular as the US. In Europe people travel across borders and speak multiple languages all the time, and yet it's like pulling teeth to put together multiple regional subtitle rights for use in a country where it is not the native language. For someone to subscribe to Netflix and be able to use it in multiple countries with the subtitles of their choice consistently available is a huge benefit to a huge number of affluent users. This is something which the existing film industry is incapable of doing structurally, and therefore is a huge advantage that can only be replicated by the biggest producers (ie. major studios). And those big companies do not have product development and UX in their DNA, so they will struggle to compete with Netflix in this regard (to date only HBO shows promise). But meanwhile the Netflix experience will be so much better that they will undermine the foundations of industry.
I'm reminded of how in 2007 no corporate IT department would allow employees to use iPhones, and even though Apple never explicitly addressed the enterprise market, and Microsoft bent over backwards to give corporate buyers what they wanted, at the end of the day companies which didn't allow their employees to use their iPhones for work suffered a competitive disadvantage.
It is quite possible that this is due to licensing issues. This link here https://mrgnome.wordpress.com/2013/11/02/no-option-to-turn-o... might or might not help you, given its age.
In some sense it is still better than Amazon Prime in Germany with only German audio being available when I was using it last.
Do you know whether the same thing happens with Netflix original content as well?
BTW the problem extends beyond subtitles. International movies typically are just available in their original language + local translation (German). Then sometimes the video stream also differs from the English version (e.g. when there is a sign in German language).
But I'm not sure any of the partners in the conventional setup have a reason to change. US networks don't care about worldwide rights. Producers don't care who is paying them for the rights. Other country networks like having content to license.