Great question — answering as the UphillTech team:
Some of it may depend on the region/country which the original translation was created and where the second company's region is. In the U.S., translations are derivative works, which are copyrighted separately themselves but cannot be produced without the consent of the original work's copyright holder. And because the reason for doing the translation and distribution (be it streaming or physical media) is to localize for a region's consumers, there's usually no reason to need a new translation but it ultimately depends on the original copyright holder. Sometimes, simulcast streams have translations that were done under a heavier time constraint, even if the scripts are shared to the...
Full answer by Jon Lin: https://anime.stackexchange.com/a/20830 (CC BY-SA 3.0).
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